IEC 60821:1991/Amd 1:1999

VMEbus - Microprocessor system bus for 1 byte to 4 byte data - Amendment 1

Bus VMEbus — Bus système à microprocesseurs pour données à 1 octet à 4 octets — Amendement 1

General Information

• Status: Published
• Publication Date: 14-Jan-1999
• ICS: 31.080.01 - Semiconductor devices in general
• ICS: 35.160 - Microprocessor systems
• ICS: 35.200 - Interface and interconnection equipment
• Technical Committee: ISO/IEC JTC 1/SC 25 - Interconnection of information technology equipment
• Drafting Committee: ISO/IEC JTC 1/SC 25 - Interconnection of information technology equipment
• Current Stage: 6060 - International Standard published
• Start Date: 15-Jan-1999
• Due Date: 16-Jul-2000
• Completion Date: 15-Jan-1999

Relations

• Amends: IEC 60821:1991 - VMEbus - Microprocessor system bus for 1 byte to 4 byte data
• Effective Date: 22-May-2021

Overview

IEC 60821:1991/Amd 1:1999 is Amendment 1 to the IEC VMEbus specification for microprocessor system buses handling 1‑byte to 4‑byte data. Prepared by ISO/IEC JTC1/SC26 and published by the IEC, this amendment updates signal definitions, data‑transfer rules, arbitration and interrupt naming/behavior, mechanical board requirements, and several normative and informative appendices to improve interoperability and implementation clarity for VMEbus systems.

Key topics

• Signal and timing clarifications
  • WRITE* is defined as a level‑significant signal strobed by the falling edge of the first data strobe (DSA*) and remains valid while any data strobe (DSA* or DSB*) is low.
• Data transfer capability rules
  • D08(O) slave behavior clarified: D08(O) slaves MUST NOT drive DTACK* low for certain byte-location requests (e.g., BYTE(0), BYTE(2), BYTE(1-2), etc.).
  • Tables and mnemonics updated so entries read “must accept” / “must monitor” rather than “can …”.
• Unaligned transfers (UAT)
  • Revised UAT mnemonic table specifying which masters and slaves must accept or generate particular multi‑byte read/write cycles (quad, triple, double).
• Arbitration and requester behavior
  • Naming corrections: BRO* → BR0*, BGOIN* → BG0IN*.
  • FAIR ARBITER/requester rule: after grant, a requester must monitor its request line and must not re‑issue a new bus request until its request line has been high.
• Priority interrupt bus
  • Interrupt lines renamed to IRQ1–IRQ7**; interrupt acknowledge line title standardized to IACK (asterisk removed in usages).
  • Rules and permissions for interrupt drivers clarified.
• Mechanical specifications
  • Board thickness requirement: boards MUST be 1.6 mm ± 0.2 mm (0.063 in ± 0.008 in) in the guide area.
• Appendices and metastability
  • Appendix titles updated to indicate normative/informative status.
  • Metastability/resynchronisation guidance updated; delay “F” should cover metastability resolution at the selected MTBF plus grant logic propagation.

Applications

• Hardware and embedded systems engineers implementing or verifying VMEbus motherboards, backplanes and modules.
• System integrators and test labs performing compliance, interoperability and conformance testing.
• Firmware and low‑level software teams coordinating timing, interrupt handling and bus arbitration behavior.
• Standards managers and procurement teams referencing mechanical and signaling requirements for VMEbus hardware.

Related standards

• This amendment is part of the broader VMEbus family and was prepared under ISO/IEC JTC 1/SC 26. Implementers should review the base IEC 60821:1991 document and other VMEbus specifications for complete compliance context.

Keywords: IEC 60821, VMEbus, amendment 1, microprocessor system bus, data transfer, unaligned transfers, arbitration, priority interrupt bus, board thickness, interoperability, compliance.

Standards Content (Sample)

NORME CEI
INTERNATIONALE
IEC
INTERNATIONAL
STANDARD
AMENDEMENT 1
AMENDMENT 1
1999-01
Amendment 1
VMEbus –
Microprocessor system bus
for 1 byte to 4 byte data
Amendement 1
Bus VMEbus –
Bus système à microprocesseurs
pour données de 1 octet à 4 octets
 IEC 1999 Droits de reproduction réservés  Copyright - all rights reserved
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: [phone] e-mail: [e-mail] IEC web site http: //www.iec.ch
CODE PRIX
Commission Electrotechnique Internationale
PRICE CODE J
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue

– 2 – 60821 Amend. 1 © IEC:1999(E)
FOREWORD
This amendment has been prepared by subcommittee 26: Microprocessor systems, of the Joint
Technical Committee ISO/IEC JTC 1: Information technology.
The text of this amendment is based on the following documents:
Text Report on voting
ISO/IEC JTC1/SC 26 N 237 ISO/IEC JTC1/SC 26 N 218
Full information the voting for the approval of this amendment can be found in the report on
voting indicated in the above table.
___________
CHAPTER 2: IEC 60821 BUS DATA TRANSFER BUS
Page 67
2.2.4.5 WRITE*
Replace the first sentence of this subclause by the following:
WRITE* is a level significant signal line that is strobed by the falling edge of the first data
strobe (DSA*) and is valid as long as any data strobe (DSA* or DSB*) is low.
Page 89
2.3.6 Basic data transfer capabilities
Replace Rule 2.65 by the following:
D08(O) SLAVES MUST NOT respond by driving DTACK* low during cycles that request access
to byte locations BYTE(0), BYTE(2), BYTE(1-2), BYTE(2-3), BYTE(0-2), BYTE(1-3), or
BYTE(0-3).
Insert, at the end of Suggestion 2.8, the following text:
4) When a D08(O) SLAVE is requested to do a BYTE(0) or BYTE(2) transfer.
Page 93
Table 2-10 – Mnemonics that specify basic data transfer capabilities
Replace in the third column the words "can accept" and "can monitor" by "must accept" and
"must monitor".
60821 Amend. 1 © IEC:1999(E) – 3 –
2.3.7 Block transfer capabilities
Add, on page 95, at the end of Rule 2.12, the words "in the address space."
Replace, on page 97, at the end of the first sentence of Observation 2.87, "D08-D15" by
"D00-D15".
Page 99
Table 2-11 – Mnemonic that specifies block transfer capabilities
Replace, in the third column, the words "Can accept" and "Can monitor" by "Must accept" and
"Must monitor".
Page 101
Table 2-12 – Mnemonic that specifies read-modify-write capabilities
Replace, in the third column, the words "Can accept" and "Can monitor" by "Must accept" and
"Must monitor".
Page 103
2.3.9 Unaligned transfer capabilities
Page 105
Table 2-13 – Transferring 32 bits of data using multiple byte transfer cycles
Replace, in row B, line 3, and line 6, "Group 1, BYTE(0)" by "GROUP 2, BYTE(0)".
Replace, in row D, line 6, "D00-D23" by "D00-D07".
Page 107
Table 2-14 – Transferring 16 bits of data using multiple byte transfer cycles
Replace, in row F, line 1, "D08-D15" by "D00-D07".
Replace, in row F, line 2, "D16-D23" by "D08-D15".
RULE 2.6
Replace, at the beginning of the sentence, "D08(0)" by "D08(O)"
Replace the text before table 2-15 and after RULE 2.6 by:
Table 2-15 lists how the unaligned transfer (UAT) mnemonic is used to describe MASTERS
and SLAVES.
– 4 – 60821 Amend. 1 © IEC:1999(E)
Table 2-15 – Mnemonic that specifies unaligned transfer capability
Replace table 2-15 by the following revised table:
The following mnemonic When applied to a Means that it
UAT D32 MASTER Can generate the following cycles:
D32 SLAVE MUST accept the following cycles:
Quad byte read cycles:
BYTE(0-3) READ
Quad byte write cycle:
BYTE (0-3) WRITE
Triple byte read cycles:
BYTE(0-3) READ
BYTE(1-3) READ
Triple byte write cycles:
BYTE(0-2) WRITE
BYTE(1-3) WRITE
Double byte read cycles:
BYTE(1-2) READ
Double byte write cycles:
BYTE(1-2) WRITE
Page 109
Table 2-16 – Mnemonic that specifies ADDRESS-ONLY capability
Replace, in the first column, "AD0" by "ADO".
Page 133
Table 2-17 – Timing diagrams that define MASTER, SLAVE and LOCATION MONITOR
operation
Replace, in the first row of the first column, "AD0" by "ADO".
Page 135
Table 2-18 – Definitions of mnemonics used in tables 2-19, 2-20 and 2-21
Replace, in the seventh row, "DRIVEN BY SLAVE" by "DRIVEN BY SLAVE?".
Page 139
Table 2-20 – Use of DS1*, DS0*, AO1 and LWORD* during the various cycles
Replace, in the first row, "AD0" by "ADO".

60821 Amend. 1 © IEC:1999(E) – 5 –
Page 141
Table 2-21 – Use of the data lines to transfer data
Replace, in the first row, "AD0" by "ADO".
CHAPTER 3: IEC 60821 BUS DATA TRANSFER BUS
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