To:	Users
From:	Bob Supnik
Subj:	IBM 1620 Simulator Usage
Date:	15-Sep-2005

			COPYRIGHT NOTICE

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

   Original code published in 1993-2005, written by Robert M Supnik
   Copyright (c) 1993-2005, Robert M Supnik

   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
   ROBERT M SUPNIK 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 name of Robert M Supnik shall not be
   used in advertising or otherwise to promote the sale, use or other dealings
   in this Software without prior written authorization from Robert M Supnik.

This memorandum documents the IBM 1620 simulator.  This simulator is based on
Geoff Kuenning's 1620 simulator, which is used by permission.

1. Simulator Files

sim/		scp.h
		sim_console.h
		sim_defs.h
		sim_fio.h
		sim_rev.h
		sim_sock.h
		sim_timer.h
		sim_tmxr.h
		scp.c
		sim_console.c
		sim_fio.c
		sim_sock.c
		sim_timer.c
		sim_tmxr.c

sim/i1620/	i1620_defs.h
		i1620_cpu.c
		i1620_fp.c
		i1620_tty.c
		i1620_pt.c
		i1620_cd.c
		i1620_lp.c
		i1620_dp.c
		i1620_sys.c	

2. IBM 1620 Features

The IBM 1620 simulator is configured as follows:

device		simulates
name(s)

CPU		IBM 1620 Model 1 or Model 2 CPU with 20K to 60K of memory
		Model 1 options: indirect addressing, automatic divide,
		   edit instructions, floating point
		Model 2 options: indexing, binary capability, floating point
TTY		IBM console terminal
PTR		IBM 1621 paper tape reader
PTP		IBM 1624 paper tape punch
CDR,CDP		IBM 1622 card reader/punch
LPT		IBM 1443 line printer
DP		IBM 1311 disk pack with four drives

The IBM 1620 simulator implements many unique stop conditions.  On almost
any kind of error the simulator stops:

	unimplemented opcode
	reference to non-existent device
	invalid digit
	invalid alphameric character
	invalid P address digit
	invalid Q address digit
	indirect address limit exceeded
	invalid odd address
	invalid even address
	invalid function
	invalid indicator
	invalid return address register
	skip to unpunched carriage control tape channel
	card reader hopper empty
	overflow with arithmetic stop switch set
	I/O error with I/O stop switch set
	invalid disk drive
	invalid disk sector address
	invalid disk sector count
	invalid disk buffer address
	disk address compare error
	disk cylinder overflow error
	disk write check error
	field exceeds memory
	record exceeds memory
	floating point mantissa exceeds maximum length
	floating point mantissas not the same length
	floating point exponent check with arithmetic stop switch set
	floating point exponent missing high flag

The LOAD command is used to load a line printer carriage-control tape.
The DUMP command is not implemented.

2.1 CPU

The CPU options include the CPU model (Model 1 or Model 2), a number of
special features, and the size of main memory.

	SET CPU IA		enable indirect addressing
	SET CPU NOIA		disable indirect addressing
	SET CPU EDT		enable extra editing instructions
	SET CPU NOEDT		disable extra editing instructions
	SET CPU DIV		enable divide instructions
	SET CPU NODIV		disable divide instructions
	SET CPU IDX		enable indexing
	SET CPU NOIDX		disable indexing
	SET CPU BIN		enable binary instructions
	SET CPU NOBIN		disable binary instructions
	SET CPU FP		enable floating point instructions
	SET CPU NOFP		disable floating point instructions
	SET CPU MOD1		set Model 1
	SET CPU MOD2		set Model 2
	SET CPU 20K		set memory size = 20K
	SET CPU 40K		set memory size = 40K
	SET CPU 60K		set memory size = 60K

Model 1 options include IA, EDT, DIV, and FP; the first three are on by
default.  Model 2 options include IDX, BIN, and FP; IA, EDT, and DIV are
standard on the Model 2.

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.  Initially, the CPU is a Model 1, memory size is
20K, and indirect addressing, editing instructions, and divide are enabled.

Memory is implemented as 5 bit BCD digits, as follows:

	4	3	2	1	0

	flag	8	4	2	1
		<-------- digit -------->

In BCD, the decimal digits 0-9 are (hex) values 0x0, 0x1, 0x2, 0x3, 0x4,
0x5, 0x6, 0x7, 0x8, 0x9, respectively.  0xA is record mark, 0xC non-
punching blank, and 0xF group mark, respectively.

CPU registers include the visible state of the processor.  The 1620 has no
interrupt system.

	name		size	comments

	IR1		16	instruction storage address register (PC)
	IR2		16	return register
	PR1		16	processor register 1
	PAR		16	P address register (OR2)
	QAR		16	Q address register (OR1)
	SS1		1	sense switch 1
	SS2		1	sense switch 2
	SS3		1	sense switch 3
	SS4		1	sense switch 4
	HP		1	high/positive indicator
	EZ		1	equal/zero indicator
	ARCHK		1	arithmetic check (overflow) indicator
	EXPCHK		1	exponent check indicator
	RDCHK		1	read check indicator
	WRCHK		1	write check indicator
	ARSTOP		1	arithmetic check stop switch
	IOSTOP		1	I/O check stop switch
	IND[0:99]	1	indicator array
	IAE		1	indirect address enable (Model 2 only)
	IDXE		1	indexing enable (Model 2 only)
	IDXB		1	indexing band select (Model 2 only)
	IR1Q[0:63]	16	IR1 prior to last branch;
				most recent IR1 change first
	WRU		8	interrupt character

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.

2.2 Console Typewriter (TTY)

The console typewriter (TTY) is a half-duplex console.  The typewriter
registers are:

	name		size	comments

	COL		7	current column
	TIME		24	polling interval

When the 1620 CPU requests input from the keyboard, a greater than sign
(>) is printed.  The CPU hangs waiting for input until the return/enter
key is pressed.  The typewriter has no errors.

2.3 1621 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 starts the
standard paper tape boot sequence at location 0.

The paper tape reader implements these registers:

	name		size	comments

	POS		32	position in the input file

Error handling is as follows:

	error	      IOCHK	processed as

	not attached	x	set RDCHK indicator, report error, stop

	end of file	x	set RDCHK indicator, report error, stop

	OS I/O error	x	set RDCHK indicator, report error, stop

	parity error	1	set RDCHK indicator, report error, stop
			0	set RDCHK indicator

2.4 1624 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 paper tape punch implements these registers:

	name		size	comments

	POS		32	position in the output file

Error handling is as follows:

	error	      IOCHK	processed as

	not attached	x	set WRCHK indicator, report error, stop

	OS I/O error	x	set WRCHK indicator, report error, stop

	invalid char	1	set WRCHK indicator, report error, stop
			0	set WRCHK indicator

2.5 1622 Card Reader/Punch (CDR, CDP)

The IBM 1402 card/reader punch is simulated as two independent devices:
the card reader (CDR) and the card punch (CDP).

The card reader supports the BOOT command.  BOOT CDR starts the standard
card boot sequence at location 0.

The card reader reads data from a disk file, while the punch writes data
to a disk file.  Cards are simulated as ASCII text lines with terminating
newlines.  For each unit, 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 these devices.

The card reader registers are:

	name		size	comments

	LAST		1	last card indicator
	POS		32	position

The card punch registes are:

	name		size	comments

	POS		32	position

Card reader error handling is as follows:

	error	      IOCHK	processed as

	end of file	x	set RDCHK indicator, report error, stop

	not attached	x	set RDCHK indicator, report error, stop

	OS I/O error	x	set RDCHK indicator, report error, stop

	invalid char	1	set RDCHK indicator, report error, stop
			0	set RDCHK indicator

Card punch error handling is as follows:

	error	      IOCHK	processed as

	not attached	x	set WRCHK indicator, report error, stop

	OS I/O error	x	set WRCHK indicator, report error, stop

	invalid char	1	set WRCHK indicator, report error, stop
			0	set WRCHK indicator

2.6 1443 Line Printer (LPT)

The IBM 1443 line printer (LPT) writes its data, converted to ASCII, to
a disk file.  The line printer can be programmed with a carriage control
tape.  The LOAD command loads a new carriage control tape:

	LOAD <file>		load carriage control tape file

The format of a carriage control tape consists of multiple lines.  Each
line contains an optional repeat count, enclosed in parentheses, optionally
followed by a series of column numbers separated by commas.  Column numbers
must be between 1 and 12; a column number of zero denotes top of form.  The
following are all legal carriage control specifications:

	<blank line>		no punch
	(5)			5 lines with no punches
	1,5,7,8			columns 1, 5, 7, 8 punched
	(10)2			10 lines with column 2 punched
	1,0			column 1 punched; top of form

The default form is 66 lines long, with column 1 and the top of form mark
on line 1, and the rest blank.

The line printer registers are:

	name		size	comments

	LBUF[0:119]	7	line buffer
	BPTR		7	buffer pointer
	PCTL		8	saved print control directive
	PRCHK		1	print check indicator
	PRCH9		1	channel 9 indicator
	PRCH12		1	channel 12 indicator
	POS		32	position
	CCT[0:131]	32	carriage control tape array	
	CCTP		8	carriage control tape pointer
	CCTL		8	carriage control tape length (read only)

Error handling is as follows:

	error	      IOCHK	processed as

	not attached	x	set PRCHK, WRCHK indicators, report error, stop

	OS I/O error	x	set PRCHK, WRCHK indicators, report error, stop

	invalid char	1	set PRCHK, WRCHK indicator, report error, stop
			0	set PRCHK, WRCHK indicator

2.7 1311 Disk Pack (DP)

The disk pack controller supports 4 drives, numbered 0 through 3.  Disk
pack options include the ability to enable address writing (formatting).

	SET DPn ADDROFF		set unit n address enable off
	SET DPn ADDRON		set unit n address enable on

Units can also be set ENABLED or DISABLED.

Unlike most simulated disks, the 1311 includes explicit representation
for sector addresses.  This is to support non-standard formats, such as
the inclusion of the drive number in the sector address.  As a result,
1311 sectors are 105 digits long: 5 address digits and 100 data digits.
If the 1311 has not been formatted, the addresses are zeroes and are
synthesized, if needed, based on the sector number. 

The disk pack controller implements these registers:

	name		size	comments

	ADCHK		1	address check (compare error) indicator
	WLRC		1	wrong length record check indicator
	CYLO		1	cylinder overflow check indicator
	ERR		1	disk error indicator
	DPSTOP		1	disk check stop

Error handling is as follows:

	error	      DPCHK	processed as

	not attached	x	set ERR indicator, report error, stop

1311 data files are buffered in memory; therefore, end of file and OS
I/O errors cannot occur.

2.8 Symbolic Display and Input

The IBM 1620 simulator implements symbolic display and input.  Display is
controlled by command line switches:

	-c			display as single character (alphameric
				for CPU and DP, ASCII for others)
	-s			display as flag terminated alphameric string
				(CPU and DP only)
	-m			display instruction mnemonics
				(CPU and DP only)
	-d			display 50 characters per line, with word
				marks denoted by "_" on the line above

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

	' or -c			character (alphameric for CPU and DP, ASCII
				for others)
	" or -s			alphameric string (CPU and DP only)
	alphabetic		instruction mnemonic (CPU and DP only)
	numeric			octal number

Instruction input is free format and consists of an opcode and up to
three operands:

	op {+/-}ppppp{(idx)},{+-}qqqqq{(idx)},flags

The p address and, if present, the q address, are always decimal.  A
plus sign is ignored; a minus sign denotes indirect addressing (or a
negative immediate operand).  If indexing is enabled, addresses may
be indexed; index registers are decimal numbers between 1 and 7.  The
flags field is used to set extra flags on the instruction.  It consists
of digit numbers in ascending order, with no separators.  For example,

	AM -12345(5),67890,110

translates into
	 _ _ ___  _
	111234567890

The flag over digits 3 and 5 specify the P index register; the flag
over digit 6 specifies the P indirect address; the flag over digit 7
marks the end of the immediate Q operand; and the flags over digits
1 and 10 are specified by the third field.

2.9 Character Sets

The IBM 1620 uses single digits to represent numbers, and pairs of
digits to represent characters (alphameric coding).  Only a small
number of the 256 possible alphameric codings have legitimate values.
Further, the translation between alphameric and devices varied from
device to device.  The simulator implements a code called 1620 ASCII,
which allows all 64 possible card codes to be represented by upper
case ASCII characters.  In addition, lower case alphabetic characters
are accepted on input as equivalent to upper case.

Card code	PT code	RA	RN	LPT WA	ASCII representation

<blank>		C	0	0	blank	blank
1		1	71	1	1	1
2		2	72	2	2	2
3		C21	73	3	3	3
4		4	74	4	4	4
5		C41	75	5	5	5
6		C42	76	6	6	6
7		421	77	7	7	7
8		8	78	8	8	8
9		C81	79	9	9	9
2 + 8		C82	? 0A	A	na	^
3 + 8		821	33	B	=	= (or #)
4 + 8		C84	34	C	@	@ (or ')
5 + 8		841	70	0	0	:
6 + 8		842	? 0E	E	na	>
7 + 8		C8421	? 0F	F	na	{
12		XOC	10	0	+	+ (or &)
12 + 1		XO1	41	1	A	A
12 + 2		XO2	42	2	B	B
12 + 3		XOC21	43	3	C	C
12 + 4		XO4	44	4	D	D
12 + 5		XOC41	45	5	E	E
12 + 6		XOC42	46	6	F	F
12 + 7		XO421	47	7	G	G
12 + 8		XO8	48	8	H	H
12 + 9		XOC81	49	9	I	I
12 + 2 + 8	XOC82	? 5A	? F+A	na	?
12 + 3 + 8	XO821	3	? F+B	.	.
12 + 4 + 8	XOC84	4	C	)	)
12 + 5 + 8	XO841	40	0	na	[
12 + 6 + 8	XO842	? 5E	? F+E	na	<
12 + 7 + 8	XOC8421	5F	F+F	na	}
11		X	20	F+0	-	-
11 + 1		XC1	51	F+1	J	J
11 + 2		XC2	52	F+2	K	K
11 + 3		X21	53	F+3	L	L
11 + 4		XC4	54	F+4	M	M
11 + 5		X41	55	F+5	N	N
11 + 6		X42	56	F+6	O	O
11 + 7		XC421	57	F+7	P	P
11 + 8		XC8	58	F+8	Q	Q
11 + 9		X81	59	F+9	R	R
11 + 2 + 8	X82	5A	F+A	na	!
11 + 3 + 8	XC821	13	F+B	$	$
11 + 4 + 8	X84	14	F+C	*	*
11 + 5 + 8	XC841	50	F+0	-	]
11 + 6 + 8	XC842	? 5E	? F+E	na	;
11 + 7 + 8	X8421	5F	F+F	na	_
0		O	70	0	0	0
0 + 1		OC1	21	1	/	/
0 + 2		OC2	62	2	S	S
0 + 3		O21	63	3	T	T
0 + 4		OC4	64	4	U	U
0 + 5		O41	65	5	V	V
0 + 6		O42	66	6	W	W
0 + 7		OC421	67	7	X	X
0 + 8		OC8	68	8	Y	Y
0 + 9		O81	69	9	Z	Z
0 + 2 + 8	O82	0A	A	na	|
0 + 3 + 8	OC821	23	B	,	,
0 + 4 + 8	O84	24	C	(	( (or %)
0 + 5 + 8	OC841	60	0	na	~
0 + 6 + 8	OC842	0E	E	na	\
0 + 7 + 8	O8421	0F	F	na	"

			2		?	
			12		!	
			22		|	
			32		0	
			35		:	
			36		blank	
11 + 0			50		-	`
