B5000 instruction set

Syllable repertoire for B5000, B5500 and B5700

Not to be confused with Burroughs B6x00-7x00 instruction set.

See also: Burroughs large systems § B5000

This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages)

This article provides insufficient context for those unfamiliar with the subject. Please help improve the article by providing more context for the reader. (July 2020) (Learn how and when to remove this message)

|

This article relies excessively on references to primary sources. Please improve this article by adding secondary or tertiary sources.
Find sources: "B5000 instruction set" – news · newspapers · books · scholar · JSTOR (July 2020) (Learn how and when to remove this message)

|

(Learn how and when to remove this message)

The Burroughs B5000 was the first stack machine and also the first computer with a segmented virtual memory. The Burroughs B5000 instruction set includes the set of valid operations for the B5000, B5500 and B5700. It is not compatible with the B6500, B7500, B8500 or their successors.

Instruction streams on a B5000 contain 12-bit syllables, four to a word. The architecture has two modes, Word Mode[1][2] and Character Mode,[3][4] and each has a separate repertoire of syllables. A processor may be either Control State or Normal State, and certain syllables are only permissible in Control State. The architecture does not provide for addressing registers or storage directly; all references are through the 1024 word Program Reference Table (PRT), current code segment, marked locations within the stack or to the A and B registers holding the top two locations on the stack. Burroughs numbers bits in a syllable from 0 (high bit) to 11 (low bit) and in a word from 0 (high bit) to 47 (low bit).

## Word Mode

[edit]

In Word Mode, there are four types of syllables.

B5x00 Word Mode Syllables[5] Bits
10-11  | Syllable Type  | Bits 0-9[6]

|
|

0  | Literal Call  | integer value
1  | Opcode  | Operation
2  | Operand Call  | Relative address
3  | Descriptor Call  | Relative address

The interpretation of the 10-bit relative address in Operand Call and Descriptor Call depends on the setting of several processor flags. For main programs (SALF off) it is always an offset into the Program Reference Table (PRT).

B5x00 Relative Addressing[7] SALF[a] | T0
A38  | T1
A39  | T2
A40  | MSFF[b] | Base  | Contents  | Index Sign  | Index
Bits[c] | Max
Index

|
|
|
|
|
|
|
|
|

OFF  | \-  | \-  | \-  | \-  | R  | Address of PRT  | \+  | T 0-9
A 38-47  | 1023
ON  | OFF  | \-  | \-  | \-  | R  | Address of PRT  | \+  | T 1-9
A 39-47  | 511
ON  | ON  | OFF  | \-  | OFF  | F  | Address of last RCW[d] or MSCW[e] on stack  | \+  | T 2-9
A 40-47  | 255
ON  | ON  | OFF  | \-  | ON  | (R+7)[f]
Bits 18-32  | F register from MSCW[e] at PRT+7  | \+  | T 2-9
A 40-47  | 255
ON  | ON  | ON  | OFF  | \-  | C[g] | Address of current instruction word  | \+  | T 3-9
A 41-47  | 127
ON  | ON  | ON  | ON  | OFF  | F  | Address of last RCW[d] or MSCW[e] on stack  | \-  | T 3-9
A 41-47  | 127
ON  | ON  | ON  | ON  | ON  | (R+7)[f]
Bits 18-32  | F register from MSCW[e] at PRT+7  | \-  | T 3-9
A 41-47  | 127
Notes:

1. ^ SALF Subroutine Level Flipflop
2. ^ MSFF Mark Stack FlipFlop
3. ^ For Operand Call (OPDC) and Descriptor Call (DESC) syllables, the relative address is bits 0-9 (T register) of the syllable. For Store operators (CID, CND, ISD, ISN, STD, STN), the A register (top of stack) contains an absolute address if the Flag bit is set and a relative address if the Flag bit is off.
4. ^ a b RCW Return Control Word
5. ^ a b c d MSCW Mark Stack Control Word
6. ^ a b F register from MSCW at PRT+7
7. ^ C (current instruction word)-relative forced to R (PRT)-relative for Store, Program and I/O Release operators

## Character Mode

[edit]

This section needs expansion. You can help by adding to it. (February 2023)

|

## References

[edit]

1. ^ "5 Word Mode Operation", Burroughs B5500 Information Processing Systems Reference Manual (PDF), Systems Documentation, Burroughs Corporation, May 1967, pp. 5-1–5-21, 1021326
2. ^ "6 Word Mode Syllables and Operators", Burroughs B5500 Information Processing Systems Reference Manual (PDF), Systems Documentation, Burroughs Corporation, May 1967, pp. 6-1–6-32, 1021326
3. ^ "7 Character Mode Operation", Burroughs B5500 Information Processing Systems Reference Manual (PDF), Systems Documentation, Burroughs Corporation, May 1967, p. 7-1  - 7-7, 1021326
4. ^ "8 Character Mode Operators", Burroughs B5500 Information Processing Systems Reference Manual (PDF), Systems Documentation, Burroughs Corporation, May 1967, p. 8-1  - 8-9, 1021326
5. ^ "5.5. Syllable Type", Burroughs B5500 Information Processing Systems Reference Manual (PDF), Systems Documentation, Burroughs Corporation, May 1967, p. 5-2, 1021326.
6. ^ "5.6. Bits 0-9", Burroughs B5500 Information Processing Systems Reference Manual (PDF), Systems Documentation, Burroughs Corporation, May 1967, p. 5-2, 1021326.
7. ^ "5.9. Relative Addressing", Burroughs B5500 Information Processing Systems Reference Manual (PDF), Systems Documentation, Burroughs Corporation, May 1967, p. 5-4, 1021326

This computer hardware article is a stub. You can help Wikipedia by expanding it.

|

* v
* t
* e

*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template