IEEE 1149.5 MTM Bus：模块测试与维护协议详解

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IEEE Std 1149.5-1995《模块测试与维护总线（MTM-Bus）规范》是由IEEE计算机协会的测试技术标准委员会所制定，于1995年8月14日获得批准。这个标准定义了一种串行、背板式的测试和维护总线（MTM-Bus），旨在将来自不同设计团队或供应商的模块整合到可测试和可维护的子系统中。它关注于物理层、链路层和命令层的设计，提供基础的模块测试和维护功能。在物理层，标准定义了MTM-Bus的电气接口和信号特性，确保数据传输的可靠性和一致性。链路层则负责处理数据包的发送和接收，包括错误检测和恢复机制，以保证通信的高效性。命令层则是核心，它规定了一系列通用的命令集，使得测试工程师能够对模块进行初始化、配置、读取状态和执行自检操作。 MTM-Bus支持边界扫描（Boundary Scan），这是一种内置自测技术，通过总线上的特定信号实现对模块内部电路的逐个检查，有助于诊断和隔离故障。此外，它还允许访问模块内的资源，如内存、外设等，以便深入进行模块性能测试和维护。标准还包括了用于故障隔离和模块间背板连接测试的功能，这对于系统的整体诊断和维护至关重要。通过MTM-Bus，系统级的系统诊断和测试得以实现，从而提高了整个子系统的可靠性和效率。总结来说，IEEE 1149.5 MTM-Bus规范是电子和电气工程领域的一个重要标准，它不仅简化了模块间的集成测试流程，而且提供了强大的工具来支持硬件故障检测、预防性维护和系统健康监控，对于现代电子产品制造和维护有着深远的影响。

IEEE

Std

49.5-1 995

IEEE

STANDARD FOR MODULE TEST AND

The Physical Layer requirements

specify the physical interconnections that comprise the bus. This includes

the specification of

the

minimum requirements regarding physical interconnections, signal characteristics,

and timing characteristics. The minimum requirements for the Physical Layer are specified in clause 4. The

Physical Layer characteristics that are specific to system technology

are

not defined in this Standard.

The architecture

of the MTM-Bus and its addressing scheme

are

specified in clause

The

Link

Layer requirements

specify the protocol features that permit error-free packet transfer between the

MTM-Bus Master and one or more MTM-Bus Slaves. These features include

serialization/packetization

information, parity generation and checking, and address recognition. The Link Layer

also

provides for the

multiplexing

data and control functions on single wires. The requirements for the Link Layer are specified

in clauses

through 11 of this Standard.

Message

Layer

Applications

Master

Link

Layer

Message Applications

Layer

Physical Layer

NOTE-The MTM-Bus protocol includes Physical Layer, Link Layer, and Message Layer protocols.

Figure l-5-Protocol layers

Message layer requirements

specify

thc

SYllIilY

for

inessages and id

fies the functions that have to or can

be supported by the MTM-Bus Mastcr

klTM

Bus

Slaves. Requirements for the Message Layer are speci-

fied in clauses 12 through 20.

Port requirements

describe a set of recommended

permitted data sourcesldestinations (called ports) that

may be useful in some S-modules. A port may be

simple

a register

as complex as an application

interfacing this Standard to an on-module test bus. Data is transferred to/from ports during execution of Data

Transfer class (15.1.1; clause 17) commands. Requirements for ports

are

found

clause 21. Requirements

for recommended ports interfacing

MTM-Bus

the

IEEE

Std

1149.1

test bus are found in clauses 21.10

through 21.12.

Documentation requirements

are to be found in clause 22.

1.6

Extensions to this Standard

The basic protocol defined herein for the MTM-Bus may be extended to meet the needs of specific applica-

tions-as detailed

the recommendations

and

permissions.

These

extensions

may

address

such

areas

fault tolerance, electrical characteristics, and others that

allow

the

I~fr'M-Bus

to be adapted

user applica-

tions.

An example

one of these MTM-Bus-based extensions

a test and maintenance bus system for avionics

applications that

being developed by the Society of Automotive Engineers

(SAE)

Avionics Systems Divi-

sion members (see SAE AS4765).' This system

will

contain dual MTM-Buses (2

sets

5-wire

MTM-

'Information

references

can

found

2.4.

1-6

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IEEE

Std

1149.5-1995

Conventions,

definitions,

and

references

2.1

Document outline

Bus

protocols such as that defined by this Standard

are

more easily understood if their specifications are

accompanied by general descriptive material that places the details of the various parts of the protocol in

perspective and provides implementation examples. Clause

contains

overview of the application of

this

Standard to test and maintenance of electronics subsystems. Clause 2 contains reference information that

should be helpful in interpreting the subsequent clauses of the Standard. Clauses

through 22 contain the

specifications for particular features of

this

Standard. The two classes of material contained in clauses

through 22 are described in 2.1

and 2.1.2.

2.1.1 Specifications

Subclauses entitled “Specifications” contain the rules, recommendations, and permissions that define this

Standard:

Rules specify the mandatory aspects of

this

Standard. Specifications that are rules contain the word

shall.

Recommendations indicate preferred practice for designs that seek to conform to this Standard. Specifica-

tions that are recommendations contain the word

should.

Permissions

show how optional features may be introduced into a design that seeks to conform to this Stan-

dard. These features will extend the application of the protocol defined by the Standard. Specifications that

are permissions contain the word

may.

2.1.2 Descriptions

Material not contained in subclauses entitled “Specifications” is descriptive material that illustrates the need

for the features being specified, an example

their application, or other relevant information.

This

material

includes bus packet or message sequences or schematic t illustrate a possible implementation of the

specifications in this Standard. The descriptive material discusses design decisions made during the

development of this Standard.

NOTE-The descriptive material contained in this Standard

for illustrative purposes only and does not define

a preferred implementation.

2.2

Conventions

The following conventions are used in

this

Standard:

The rules, recommendations, and permissions in each Specifications subclause are contained in a

single alphabetically indexed list. References to each rule, recommendation, or permission are writ-

ten in the following form:

15.1. IC

(ii)

‘1

Subclause

number

Index

(if

any)

State and packet names defined in this Standard are written entirely in capital letters in the text

this

Standard.

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IEEE

Std

1149.5-1995

IEEE

STANDARD

FOR

MODULE

TEST

AND

A positive logic convention

used for

all

figures

this

document, i.e.,

logic

value designates

the most positive of the

two

voltages

used

for signals, including the MTM-Bus clock signal, MCLK.

When a set

related bits are denoted by

common name, the bits within the set are identified by

number with the least significant bit numbered

The identifier for a single bit in a series

related bits (e.g.,

packet) is the bit position number in

the

series enclosed in angle brackets

(“e”

and

‘5”).

The expression

<m..n>

is used

abbreviated identifier

for

a series

bits

inclusive (e.g.,

the bits in a register or packet), where

and

are

the

most

and

least

significant bits, respectively.

The phrases “signal driver(s),” “signal output(s),” and “signal input@),” when implicitly or explic-

itly refemng to MTM-Bus signals, shall

taken to refer

one

more MTM-Bus signals

exclu-

sive

MCLK unless explicitly indicated otherwise.

M-module

is used as an abbreviation for

“MTM-Bus

Master module.”

S-module

used as an abbreviation for “MTM-Bus Slave module.”

all diagrams depicting registers, packets, and data fields within registers and packets, the most

significant bit (msb)

each depicted element

assumed to

left-most within the rectangle defin-

ing the data entity.

Any reference

a figure in

this

document is intended to reference

all

drawings and text in that fig-

ure.

2.3

Definitions

The following terms are used within

this

Stantiard. Clause, subclause, table, or figure numbers are given in

parentheses

indicate specific places in the text where

terms

are discussed

detail.

2.3.1

ACKNOWLEDGE

packet:

The first packet returned

an individually addressed S-module that con-

veys to the M-module that the appropriate S-module

responding and indicates the current status

the

responding S-module

(5.3).

2.3.2 active:

When associated with a logic level (e.g.,

the word “activc-low”),

this

term identifies the

logic level to which a signal shall

set to cause a defined action

occur. When referring to an output

driver (e.g., in the phrase “an active driver”),

this

term describes

the

mode in which the driver is capable

determining the voltage of the network

which it

connected

2.3.3 amnesia address:

The module address

(‘FA’

HEX)

to which a module will respond as though

uniquely addressed if that module

(1)

i~ii~~loiiimls

thc

abilily

11~l;f~~t

wlioi

ciilmot determine its address

unambiguously and

(2)

detects that it

c‘Iiiiio1

tkki

iiiiiic.

its

atltlrcsh

on;itr~higtioiisl~

(3.3).

2.3.4 application logic:

That portion of a module that excludes the

MTM-Bus

interface logic (figure

2-1).

2.3.5 assert:

change the value of a bus signal

from

logic

(released) to logic

(asserted) or ensure that

such a signal remains at a logic

2.3.6 asserted:

Having a current value equal to logic

(said of

any

signal).

2.3.7

backplane:

Motherboard comprising

connectors

for

the

modules

a system and wiring interconnect-

ing

those modules. The intermodule wiring

the MTM-Bus is expected to

on this motherboard.

2.3.8

BMR:

Acronym for “broadcastlmulticast received.” See

2.3.10.

2.3.9 broadcast:

A mode

operation of the MTM-Bus in which

MTM-Bus Master transmits data to all

connected S-modules simultaneously throughout

message. Also, a message transmitted in this mode.

2-2

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