1. PDP-8 simulator usage

Date:

2020-05-01

Revision:

$Format:%H$

Copyright:

See LICENSE.txt for terms of use.

Copyright notice

The following copyright notice applies to the SIMH source, binary, and documentation:

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the names of The Authors shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from the Authors.

This memorandum documents the PDP-8 simulator.

1.1. Simulator files

sim/

scp.h

sim_console.h

sim_defs.h

sim_fio.h

sim_rev.h

sim_sock.h

sim_tape.h

sim_timer.h

sim_tmxr.h

scp.c

sim_console.c

sim_fio.c

sim_sock.c

sim_tape.c

sim_timer.c

sim_tmxr.c

sim/pdp8/

pdp8_defs.h

pdp8_cpu.c

pdp8_ct.c

pdp8_df.c

pdp8_dt.c

pdp8_fpp.c

pdp8_lp.c

pdp8_mt.c

pdp8_pt.c

pdp8_rf.c

pdp8_rk.c

pdp8_rl.c

pdp8_rx.c

pdp8_sys.c

pdp8_td.c

pdp8_tsc.c

pdp8_tt.c

pdp8_ttx.c

1.2. PDP-8 features

The PDP-8 simulator is configured as follows:

Device names(s)	Simulates
CPU	PDP-8/E CPU with 4KW-32KW of memory
—	KE8E extended arithmetic element (EAE)
—	KM8E memory management and timeshare control
TSC	TSC8-75 ETOS operating system timeshare control
FPP	FPP8A floating point unit
PTR,PTP	PC8E paper tape reader/punch
TTI,TTO	KL8E console terminal
TTIX,TTOX	KL8JA additional terminals, up to 16
LPT	LE8E line printer
CLK	DK8E line frequency clock (also PDP-8/A compatible)
RK	RK8E/RK05 cartridge disk controller with four drives
RF	RF08/RS08 fixed head disk controller with 1-4 platters
DF	DF32/DS32 fixed head disk controller with 1-4 platters
RL	RL8A/RL01 cartridge disk controller with four drives
RX	RX8E/RX01, RX28/RX02 floppy disk controller with two drives
DT	TC08/TU56 DECtape controller with eight drives
TD	TD8E/TU56 DECtape controller with two drives
MT	TM8E/TU10 magnetic tape controller with eight drives
CT	TA8E/TU60 cassette tape controller with two drives

Most devices can be disabled or enabled, by the commands:

SET <dev> DISABLED
SET <dev> ENABLED

The simulator allows most device numbers to be changed, by the command:

SET <dev> DEV=<number>

The PDP-8 can support only one of the set {DF32, RF08, RL8A} using the default device numbers, since they all use device numbers 60–61. The default is the RF08. To change the disk at device numbers 60-61:

SET RF DISABLED                Disable RF08
SET DF ENABLED, or             Enable DF32
SET RL ENABLED                 Enable RL8A

The PDP-8 can only support one of the set {TC08, TD8E} using the default device numbers, since both use device number 77. The default is the TC08. To change the DECtape controller to the TD8E:

SET DT DISABLED                Disable TC08
SET TD ENABLED                 Enable TD8E

The PDP-8 can only support one of the set {TM8E, TA8E} using the default device numbers, since both use device number 70. The default is the TM8E. To change the device at device number 70:

SET MT DISABLED                Disable TM8E
SET CT ENABLED                 Enable TA8E

Alternately, the device conflict can be eliminated by changing device numbers:

SET RL DEV=50
SET RL ENA
SET TD DEV=74
SET TD ENA
SET CT DEV=73
SET CT ENA

However, devices can only be BOOTed with their default device numbers.

The PDP-8 simulator implements several unique stop conditions:

• If an undefined instruction (unimplemented IOT or OPR) is decoded, and STOP_INST is set

• If a simulated DECtape runs off the end of its reel

The LOAD command supports both RIM format and BIN format tapes. If the file extension is .RIM, or the r switch is specified with LOAD, the file is assumed to be RIM format; if the file extension is not .RIM, or the -b switch is specified, the file is assumed to be BIN format. For BIN format tape loading will stop at the first trailer code (0x80). If the tape contains multiple sections specify the -a flag to load all sections on the tape. The number of sections loaded will be printed. If the tape had non-BIN format data following the last valid leader it may cause checksum errors or load unwanted data into memory.

1.2.1. CPU

The only CPU options are the presence of the EAE and the size of main memory; the memory extension and time-share control is always included, even if memory size is 4K.

SET CPU EAE                    Enable EAE
SET CPU NOEAE                  Disable EAE
SET CPU 4K                     Set memory size = 4K
SET CPU 8K                     Set memory size = 8K
SET CPU 12K                    Set memory size = 12K
SET CPU 16K                    Set memory size = 16K
SET CPU 20K                    Set memory size = 20K
SET CPU 24K                    Set memory size = 24K
SET CPU 28K                    Set memory size = 28K
SET CPU 32K                    Set memory size = 32K

If memory size is being reduced, and the memory being truncated contains non-zero data, the simulator asks for confirmation. Data in the truncated portion of memory is lost. Initial memory size is 32K.

CPU registers include the visible state of the processor as well as the control registers for the interrupt system.

Name	Size	Comments
PC	15	Program counter, including IF as high 3 bits
AC	12	Accumulator
MQ	12	Multiplier-quotient
L	1	Link
SR	12	Front panel switches
IF	3	Instruction field
DF	3	Data field
IB	3	Instruction field buffer
SF	7	Save field
UF	1	User mode flag
UB	1	User mode buffer
SC	5	EAE shift counter
GTF	1	EAE greater than flag
EMODE	1	EAE mode (0 = A, 1 = B)
ION	1	Interrupt enable
ION_DELAY	1	Interrupt enable delay for ION
CIF_DELAY	1	Interrupt enable delay for CIF
PWR_INT	1	Power fail interrupt
UF_INT	1	User mode violation interrupt
INT	15	Interrupt pending flags
DONE	15	Device done flags
ENABLE	15	Device interrupt enable flags
PCQ[0:63]	15	PC prior to last JMP, JMS, or interrupt; most recent PC change first
STOP_INST	1	Stop on undefined instruction
WRU	8	Interrupt character

The CPU attempts to detect when the simulator is idle. When idle, the simulator does not use any resources on the host system. Idle detection is controlled by the SET IDLE and SET NOIDLE commands:

SET CPU IDLE                   Enable idle detection
SET CPU NOIDLE                 Disable idle detection

Idle detection is disabled by default. At present, the CPU is considered idle if it is executing a KSF/JMP *-1 loop with interrupts disabled (OS/8, DMS-8) or a JMP * loop (TSS/8).

The CPU can maintain a history of the most recently executed instructions. This is controlled by the SET CPU HISTORY and SHOW CPU HISTORY commands:

SET CPU HISTORY                Clear history buffer
SET CPU HISTORY=0              Disable history
SET CPU HISTORY=n              Enable history, length = n
SHOW CPU HISTORY               Print CPU history
SHOW CPU HISTORY=n             Print first n entries of CPU history

The maximum length for the history is 65536 entries.

1.2.2. TSC8-75 ETOS timeshare control (TSC)

ETOS is a timeshared operating system for the PDP-8, providing multiple virtual OS/8 environments for up to 32 users. It requires a special timeshare control option, the TSC8-75. The TSC8-75 is normally disabled; to run ETOS, it must be enabled with the command:

SET TSC ENABLED

The TSC8-75 implements these registers:

Name	Size	Comments
IR	12	Most recently trapped instruction
PC	12	PC of most recently trapped instruction
CDF	1	1 if trapped instruction is CDF, 0 otherwise
ENB	1	Interrupt enable flag
INT	1	Interrupt pending flag

Except for operation of ETOS, the TSC8-75 should be left disabled.

1.2.3. FPP8A floating point unit (FPP)

The floating point unit (FPP) is an add-on device that provides floating-point capabilities. It operates as a coprocessor to the main CPU, with its own program counter and instruction set. The FPP8A is normally disabled; to use it, it must be enabled with the command:

SET FPP ENABLED

The FPP8A implements these registers:

Name	Size	Comments
FPACE	12	Floating AC exponent
FPAC0..4	12	Floating AC fraction words 0..4
CMD	12	FPP command register
STA	12	FPP status register
APTA	15	APT address pointer
APTSVF	3	APT save field
FPC	15	FPP program counter
BRA	15	Base register pointer
XRA	15	Index register pointer
OPA	15	Operand pointer
SSF	12	Single step flag
LASTLOCK	12	Last lock bit
FLAG	1	FPP flag

Except for environments that explicitly support it, the FPP8A should be left disabled.

1.2.4. Programmed I/O devices

1.2.4.1. PC8E Paper Tape Reader (PTR)

The paper tape reader (PTR) reads data from a disk file. The POS register specifies the number of the next data item to be read. Thus, by changing POS, the user can backspace or advance the reader.

The paper tape reader supports the BOOT command. BOOT PTR copies the RIM loader into memory and starts it running.

The paper tape reader implements these registers:

Name	Size	Comments
BUF	8	Last data item processed
DONE	1	Device done flag
ENABLE	1	Interrupt enable flag
INT	1	Interrupt pending flag
POS	32	Position in the input file
TIME	24	Time from I/O initiation to interrupt
STOP_IOE	1	Stop on I/O error

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Out-of-tape
End-of-file	1	Report error and stop
	0	Out-of-tape
OS I/O error	x	Report error and stop

1.2.4.2. PC8E Paper Tape Punch (PTP)

The paper tape punch (PTP) writes data to a disk file. The POS register specifies the number of the next data item to be written. Thus, by changing POS, the user can backspace or advance the punch. The default position after ATTACH is to position at the end of an existing file. A new file can be created if you attach with the -N switch.

The paper tape punch implements these registers:

Name	Size	Comments
BUF	8	Last data item processed
DONE	1	Device done flag
ENABLE	1	Interrupt enable flag
INT	1	Interrupt pending flag
POS	32	Position in the output file
TIME	24	Time from I/O initiation to interrupt
STOP_IOE	1	Stop on I/O error

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Out-of-tape
OS I/O error	x	Report error and stop

1.2.4.3. KL8E terminal input (TTI)

The terminal interfaces (TTI, TTO) can be set to one of four modes, KSR, 7B, 7B, or 8B:

Mode	Input characters	Output characters
KSR	Lowercase converted to uppercase, high-order bit set	Lowercase converted to uppercase, high-order bit cleared, non-printing characters suppressed
7P	High-order bit cleared	High-order bit cleared, non-printing characters suppressed
7B	High-order bit cleared	High-order bit cleared
8B	No changes	No changes

The default mode is KSR.

The terminal input (TTI) polls the console keyboard for input. It implements these registers:

Name	Size	Comments
BUF	8	Last data item processed
DONE	1	Device done flag
ENABLE	1	Interrupt enable flag
INT	1	Interrupt pending flag
POS	32	Number of characters input
TIME	24	Input polling interval

The terminal input is normally polled synchronously with the real-time clock. To avoid data loss, a poll is scheduled ‘TIME’ instructions after the CPU reads a character.

1.2.4.4. KL8E Terminal Output (TTO)

The terminal output (TTO) writes to the simulator console window. It implements these registers:

Name	Size	Comments
BUF	8	Last data item processed
DONE	1	Device done flag
ENABLE	1	Interrupt enable flag
INT	1	Interrupt pending flag
POS	32	Number of characters output
TIME	24	Time from I/O initiation to interrupt

1.2.4.5. LE8E Line Printer (LPT)

The line printer (LPT) writes data to a disk file. The POS register specifies the number of the next data item to be read or written. Thus, by changing POS, the user can backspace or advance the printer. The default position after ATTACH is to position at the end of an existing file. A new file can be created if you attach with the -N switch.

The line printer implements these registers:

Name	Size	Comments
BUF	8	Last data item processed
ERR	1	Error status flag
DONE	1	Device done flag
ENABLE	1	Interrupt enable flag
INT	1	Interrupt pending flag
POS	32	Position in the output file
TIME	24	Time from I/O initiation to interrupt

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Out-of-paper
OS I/O error	x	Report error and stop

1.2.4.6. DK8E Line-Frequency Clock (CLK)

The real-time clock (CLK) frequency can be adjusted as follows:

SET CLK 60HZ                   Set frequency to 60Hz
SET CLK 50HZ                   Set frequency to 50Hz
SET CLK NORMAL                 Set clock to calibrated timing
SET CLK DIAG                   Set clock to fixed timing

The default is 60Hz.

The clock implements these registers:

Name	Size	Comments
DONE	1	Device done flag
ENABLE	1	Interrupt enable flag
INT	1	Interrupt pending flag
TIME	24	Clock interval

The real-time clock autocalibrates; the clock interval is adjusted up or down so that the clock tracks actual elapsed time.

1.2.4.7. KL8JA Additional Terminals (TTIX, TTOX)

The simulator supports 1 to 16 additional terminals, with an initial default of 4 lines. The additional terminals consist of two independent devices, TTIX and TTOX. The entire set is modeled as a terminal multiplexer, with TTIX as the master controller. The number of lines is specified with a SET command:

SET TTIX LINES=n               Set number of additional lines to n [1-16]

The ATTACH command specifies the port to be used:

ATTACH TTIX <port>             Set up listening port

where port is a decimal number between 1 and 65535 that is not being used for other TCP/IP activities. The additional terminals are disabled by default.

The additional terminals can be set to one of four modes: UC, 7P, 7B, or 8B.

Mode	Input characters	Output characters
UC	Lowercase converted to uppercase, high-order bit cleared	Lowercase converted to uppercase, high-order bit cleared, non-printing characters suppressed
7P	High-order bit cleared	High-order bit cleared, non-printing characters suppressed
7B	High-order bit cleared	High-order bit cleared
8B	No changes	No changes

The default mode is UC. Finally, each line supports output logging. The SET TTOXn LOG command enables logging on a line:

SET TTOXn LOG=filename         Log output of line n to filename

The SET TTOXn NOLOG command disables logging and closes the open log file, if any.

Once TTIX is attached and the simulator is running, the terminals listen for connections on the specified port. They assume that the incoming connections are Telnet connections. The connections remain open until disconnected either by the Telnet client, a SET TTIX DISCONNECT command, or a DETACH TTIX command.

Other special commands:

SHOW TTIX CONNECTIONS  Show current connections
SHOW TTIX STATISTICS   Show statistics for active connections
SET TTOXn DISCONNECT   Disconnects the specified line

The input device (TTIX) implements these registers:

Name	Size	Comments
BUF[0:15]	8	Input buffer, lines 0 to 15
DONE	16	Device done flags (line 0 rightmost)
ENABLE	16	Interrupt enable flag
TIME	24	Initial polling interval

The input device is normally polled synchronously with the real-time clock. To avoid data loss, a poll is scheduled ‘TIME’ instructions after the CPU reads a character from any line.

The output device (TTOX) implements these registers:

Name	Size	Comments
BUF[0:15]	8	Last data item processed, lines 0-15
DONE	16	Device done flag (line 0 rightmost)
ENABLE	16	Interrupt enable flag
TIME[0:16]	24	Time from I/O initiation to interrupt, lines 0-15

The additional terminals do not support save and restore. All open connections are lost when the simulator shuts down or TTIX is detached.

1.2.4.8. TD8E/TU56 DECtape (TD)

The TD8E is a programmed I/O, non-interrupt controller, supporting two DECtape drives (0 and 1). The TD8E simulator puts a high burden on the host processor, because tape activity is simulated a line (3b) at a time. Unless the PDP-8 software requires the TD8E, the TC08 should be used to simulate DECtapes. The TD8E is disabled by default.

TD8E options include the ability to make units write-enabled or write-locked.

SET TDn LOCKED                 Set unit n write locked
SET TDn WRITEENABLED           Set unit n write enabled

Units can also be set ENABLED or DISABLED. The TD8E supports the BOOT command, but only for unit 0.

The TD8E supports supports PDP-8 format, PDP-11 format, and 18b format DECtape images. ATTACH assumes the image is in PDP-8 format; the user can force other choices with switches:

-s	PDP-11 format
-f	18b format
-a	Autoselect based on file on file size

The TD8E controller is a data-only simulator; the timing and mark track, and block header and trailer, are not stored. Thus, read always produces standard values for mark track, header, and trailer words, and write throws mark track, header, and trailer words into the bit bucket.

The TD8E controller implements these registers:

Name	Size	Comments
TDCMD	4	Command register
TDDAT	12	Data register
TDMTK	6	Mark track register
TDSLF	1	Single line flag
TDQLF	1	Quad line flag
TDTME	1	Timing error flag
TDQL	2	Quad line counter
LTIME	31	Time between lines
DCTIME	31	Time to decelerate to a full-stop
POS[0:1]	32	Position, in lines, units 0 and 1
STATT[0:1]	18	Unit state, units 0 and 1
STOP_OFFR	1	Stop on off-reel error

The LTIME parameter should not be changed, or OS/8 may fail to run correctly. The DCTIME parameter should always be at least 100 times greater than LTIME. Acceleration time is 75% of deceleration time.

1.2.4.9. TA8E/TA60 Cassette Tape (CT)

The TA8E is a programmed I/O controller supporting two cassette drives (0 and 1). The TA8E can be used with the MCPIP program under OS/8, and with the CAPS-8 operating system. Cassettes are simulated as magnetic tapes with a fixed capacity (93,000 characters). The tape format is always SimH standard. The TA8E is disabled by default.

TA8E options include the ability to make units write-enabled or write-locked.

SET CTn LOCKED                 Set unit n write locked
SET CTn WRITEENABLED           Set unit n write enabled

Units cannot be set ENABLED or DISABLED. The TA8E supports the BOOT command, but only for CAPS-8, and only for unit 0.

The TA8E controller implements these registers:

Name	Size	Comments
CTSRA	8	Status register A
CTSRB	8	Status register B
CTDB	8	Data buffer
CTDF	1	Data flag
RDY	1	Ready flag
WLE	1	Write lock error
WRITE	1	TA60 write operation flag
INT	1	Interrupt request
BPTR	17	Buffer pointer
BLNT	17	Buffer length
STIME	24	Operation start time
CTIME	24	Character latency
STOP_IOE	1	Stop on I/O errors flag
POS[0:1]	32	Position, units 0-1

Error handling is as follows:

Error	Processed as
Not attached	Tape not ready; if STOP_IOE, stop
End-of-file	Bad tape
OS I/O error	CRC error; if STOP_IOE, stop

1.2.5. Moving head disks

1.2.5.1. RK8E Cartridge Disk (RK)

RK8E options include the ability to make units write-enabled or write-locked:

SET RKn LOCKED                 Set unit n write locked
SET RKn WRITEENABLED           Set unit n write enabled

Units can also be set ENABLED or DISABLED. The RK8E supports the BOOT command.

The RK8E implements these registers:

Name	Size	Comments
RKSTA	12	Status
RKCMD	12	Disk command
RKDA	12	Disk address
RKMA	12	Current memory address
BUSY	1	Control busy flag
INT	1	Interrupt pending flag
STIME	24	Seek time, per cylinder
RTIME	24	Rotational delay
STOP_IOE	1	Stop on I/O error

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Disk not ready
End-of-file	x	Assume rest of disk is zero
OS I/O error	x	Report error and stop

1.2.5.2. RL8A Cartridge Disk (RL)

RL8A options include the ability to make units write-enabled or write-locked:

SET RLn LOCKED                 Set unit n write locked
SET RLn WRITEENABLED           Set unit n write enabled

Units can also be set ENABLED or DISABLED. The RL8A supports the BOOT command, but only for unit 0.

The RL8A implements these registers:

Name	Size	Comments
RLCSA	12	Control/status A
RLCSB	12	Control/status B
RLMA	12	Memory address
RLWC	12	Word count
RLSA	6	Sector address
RLER	12	Error flags
RLSI	16	Silo top word
RLSI1	16	Silo second word
RLSI2	16	Silo third word
RLSIL	1	Silo read left/right flag
INT	1	Interrupt request
DONE	1	Done flag
ERR	1	Composite error flag
STIME	1	Seek time, per cylinder
RTIME	1	Rotational delay
STOP_IOE	1	Stop on I/O error

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Disk not ready
End-of-file	x	Assume rest of disk is zero
OS I/O error	x	Report error and stop

1.2.6. RX8E/RX01, RX28/RX02 Floppy Disk (RX)

The RX can be configured as an RX8E with two RX01 drives, or an RX28 with two RX02 drives:

SET RX RX8E                    Set controller to RX8E/RX01
SET RX RX28                    Set controller to RX28/RX02

The controller is set to the RX8E by default. The RX28 is not backwards-compatible with the RX8E and will not work with the standard OS/8 V3D floppy disk driver.

RX8E options include the ability to set units write enabled or write locked:

SET RXn LOCKED                 Set unit n write locked
SET RXn WRITEENABLED           Set unit n write enabled

RX28 options include, in addition, the ability to set the unit density to single density, double density, or autosized; autosizing is the default:

SET RXn SINGLE                 Set unit n single density
SET RXn DOUBLE                 Set unit n double density
SET RXn AUTOSIZE               Set unit n autosize

The RX8E and RX28 support the BOOT command.

The RX8E and RX28 implement these registers:

Name	Size	Comments
RXCS	12	Status
RXDB	12	Data buffer
RXES	12	Error status
RXTA	8	Current track
RXSA	8	Current sector
STAPTR	4	Controller state
BUFPTR	8	Buffer pointer
INT	1	Interrupt pending flag
DONE	1	Device done flag
ENABLE	1	Interrupt enable flag
TR	1	Transfer ready flag
ERR	1	Error flag
CTIME	24	Command completion time
STIME	24	Seek time, per track
XTIME	24	Transfer ready delay
STOP_IOE	1	Stop on I/O error
SBUF[0:255]	8	Sector buffer array

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Disk not ready

RX01 and RX02 data files are buffered in memory; therefore, end-of-file and OS I/O errors cannot occur.

1.2.7. Fixed head disks

With default device addressing, either the RF08 or the DF32 can be present in a configuration, but not both.

1.2.7.1. RF08/RS08 Fixed Head Disk (RF)

RF08 options include the ability to set the number of platters to a fixed value between 1 and 4, or to autosize the number of platters:

SET RF 1P                      One platter (256K)
SET RF 2P                      Two platters (512K)
SET RF 3P                      Three platters (768K)
SET RF 4P                      Four platters (1024K)
SET RF AUTOSIZE                Autosized on ATTACH

The default is one platter.

The RF08 implements these registers:

Name	Size	Comments
STA	12	Status
DA	20	Current disk address
MA	12	Memory address (in memory)
WC	12	Word count (in memory)
WLK	32	Write lock switches
INT	1	Interrupt pending flag
DONE	1	Device done flag
TIME	24	Rotational delay, per word
BURST	1	Burst flag
STOP_IOE	1	Stop on I/O error

The RF08 supports the BOOT command. The default bootstrap is for OS/8. To bootstrap the 4K Disk Monitor, use the BOOT -D RF command.

The RF08 is a three-cycle data break device. If BURST = 0, word transfers are scheduled individually; if BURST = 1, the entire transfer occurs in a single data break.

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Disk not ready

RF08 data files are buffered in memory; therefore, end-of-file and OS I/O errors cannot occur.

1.2.7.2. DF32/DS32 Fixed Head Disk (DF)

DF32 options include the ability to set the number of platters to a fixed value between 1 and 4, or to autosize the number of platters:

SET DF 1P                      One platter (32K)
SET DF 2P                      Two platters (64K)
SET DF 3P                      Three platters (98K)
SET DF 4P                      Four platters (128K)
SET DF AUTOSIZE                Autosized on ATTACH

The default is one platter.

The DF32 implements these registers:

Name	Size	Comments
STA	12	Status, disk and memory address extension
DA	12	Low-order disk address
MA	12	Memory address (in memory)
WC	12	Word count (in memory)
WLK	16	Write lock switches
INT	1	Interrupt pending flag
DONE	1	Device done flag
TIME	24	Rotational delay, per word
BURST	1	Burst flag
STOP_IOE	1	Stop on I/O error

The DF32 supports the BOOT command. The default bootstrap is for OS/8. To bootstrap the 4K Disk Monitor, use the BOOT -D DF command.

The DF32 is a three-cycle data break device. If BURST = 0, word transfers are scheduled individually; if BURST = 1, the entire transfer occurs in a single data break.

Error handling is as follows:

Error	STOP_IOE	Processed as
Not attached	1	Report error and stop
	0	Disk not ready

DF32 data files are buffered in memory; therefore, end-of-file and OS I/O errors cannot occur.

1.2.8. TC08/TU56 DECtape (DT)

DT implements the TC08 DECtape controller and TU56 drives. TC08 options include the ability to make units write enabled or write locked.

SET DTn LOCKED                 Set unit n write locked
SET DTn WRITEENABLED           Set unit n write enabled

Units can also be set ENABLED or DISABLED. The TC08 supports the BOOT command, but only for unit 0.

The TC08 supports supports PDP-8 format, PDP-11 format, and 18b format DECtape images. ATTACH assumes the image is in PDP-8 format; the user can force other choices with switches:

-s	PDP-11 format
-f	18b format
-a	Autoselect based on file on file size

The TC08 controller is a data-only simulator; the timing and mark track, and block header and trailer, are not stored. Thus, the WRITE TIMING AND MARK TRACK function is not supported; the READ ALL function always returns the hardware standard block header and trailer; and the WRITE ALL function dumps non-data words into the bit bucket.

The DECtape controller implements these registers:

Name	Size	Comments
DTSA	12	Status register A
DTSB	12	Status register B
INT	1	Interrupt pending flag
ENB	1	Interrupt enable flag
DTF	1	DECtape flag
ERF	1	Error flag
CA	12	Current address (memory location 7754)
WC	12	Word count (memory location 7755)
LTIME	31	Time between lines
DCTIME	31	Time to decelerate to a full stop
SUBSTATE	2	Read/write command substate
POS[0:7]	32	Position, in lines, units 0 to 7
STATT[0:7]	31	Unit state, units 0 to 7
STOP_OFFR	1	Stop on off-reel error

It is critically important to maintain certain timing relationships among the DECtape parameters, or the DECtape simulator will fail to operate correctly.

• LTIME must be at least 6

• DCTIME needs to be at least 100 times LTIME

Acceleration time is set to 75% of deceleration time.

1.2.9. TM8E Magnetic Tape (MT)

Magnetic tape options include the ability to make units write-enabled or write-locked.

SET MTn LOCKED                 Set unit n write locked
SET MTn WRITEENABLED           Set unit n write enabled

Magnetic tape units can be set to a specific reel capacity in MB, or to unlimited capacity:

SET MTn CAPAC=m                Set unit n capacity to m MB (0 = unlimited)
SHOW MTn CAPAC                 Show unit n capacity in MB

Units can also be set ENABLED or DISABLED.

The magnetic tape controller implements these registers:

Name	Size	Comments
CMD	12	Command
FNC	12	Function
CA	12	Memory address
WC	12	Word count
DB	12	Data buffer
STA	12	Main status
STA2	6	Secondary status
DONE	1	Device done flag
INT	1	Interrupt pending flag
STOP_IOE	1	Stop on I/O error
TIME	24	Record delay
UST[0:7]	24	Unit status, units 0 to 7
POS[0:7]	32	Position, units 0 to 7

Error handling is as follows:

Error	Processed as
Not attached	Tape not ready; if STOP_IOE, stop
End-of-file	Bad tape
OS I/O error	Parity error; if STOP_IOE, stop

1.3. Symbolic display and input

The PDP-8 simulator implements symbolic display and input. Display is controlled by command-line switches:

-a	Display as ASCII character
-c	Display as two packed sixbit characters
-t	Display as two packed TSS/8 sixbit characters
-m	Display instruction mnemonics

Input parsing is controlled by the first character typed in or by command-line switches:

' or -a	ASCII character
" or -c	Two packed sixbit characters
# or -t	Two packed TSS/8 sixbit characters
Alphabetic	Instruction mnemonic
Numeric	Octal number

Instruction input uses standard PDP-8 assembler syntax. There are four instruction classes: memory reference, IOT, field change, and operate.

Memory reference instructions have the format

memref {I} {C/Z} address

where I signifies indirect, C a current page reference, and Z a zero page reference. The address is an octal number in the range 0 – 07777; if C or Z is specified, the address is a page offset in the range 0 – 177. Normally, C is not needed; the simulator figures out from the address what mode to use. However, when referencing memory outside the CPU (e.g., disks), there is no valid PC, and C must be used to specify current page addressing.

IOT instructions consist of single mnemonics, e.g., KRB, TLS. IOT instructions may be OR’d together

iot iot iot...

The simulator does not check the legality of the proposed combination. IOTs for which there is no opcode may be specified as IOT n, where n is an octal number in the range 0 – 0777.

Field change instructions (CIF, CDF) have the format

fldchg field

where field is an octal number in the range 0 – 7. Field change instructions may be OR’d together.

Operate instructions have the format

opr opr opr...

The simulator does not check the legality of the proposed combination. EAE mode A and B mnemonics may be specified regardless of the EAE mode. The operands for MUY and DVI must be deposited explicitly.