AM79C940 datasheet(45/122 Pages) AMD

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AMD

Am79C940

Internal/External Address Recognition Capabilities

PROM

M/R

EAM/R

Required Timing

Received Messages

No timing requirements

All Received Frames

No timing requirements

All Received Frames

↓

Low for 200 ns within 512-bits after SFD

Physical/Logical/Broadcast Matches

No timing requirements

Physical/Logical/Broadcast Matches

↓

Low for 200 ns within 8-bits after DA field

All Received Frames

General Purpose Serial Interface (GPSI)

The GPSI port provides the signals necessary to pre-

sent an interface consistent with the non encoded data

functions observed to/from a LAN controller such as the

Am7990 Local Area Network Controller for Ethernet

(LANCE). The actual GPSI pins are functionally identi-

cal to some of the pins from the DAI and the EADI ports,

the GPSI replicates this type of interface.

The GPSI allows use of an external Manchester en-

coder/decoder, such as the Am7992B Serial Interface

Adapter (SIA). In addition, it allows the MACE device to

be used as a MAC sublayer engine in a repeater based

on the Am79C980 Integrated Multiport Repeater (IMR).

Simple connection to the IMR Expansion Bus allows the

MAC to view all packet data passing through a number

of interconnected IMRs, allowing statistics and network

management information to be collected.

The GPSI functional pins are duplicated as follows:

Pin Configuration for GPSI Function

LANCE

MACE

Function

Type

Receive Data

RXDAT

Receive Clock

RCLK

SRDCLK

Receive Carrier Sense

RENA

RXCRS

Collision

CLSN

Transmit Data

TXDAT+

Transmit Clock

TCK

STDCLK

Transmit Enable

TENA

TXEN

IEEE 1149.1 Test Access Port Interface

An IEEE 1149.1 compatible boundary scan Test Access

Port is provided for board level continuity test and diag-

nostics. All digital input, output and input/output and in-

put/output pins are tested. Analog pins, including the

AUI differential driver (DO

±) and receivers DI±, CI±),

and the crystal input (XTAL1/XTAL2) pins, are not

tested.

The following is a brief summary of the IEEE 1149.1

compatible test functions implemented in the MACE de-

vice. For additional details, consult the IEEE Standard

Test Access Port and Boundary-Scan Architecture

document (IEEE Std 1149.1–1990).

The boundary scan test circuit requires four pins (TCK,

TMS, TDI and TDO ), defined as the Test Access Port

(TAP). It includes a finite state machine (FSM), an in-

struction register, a data register array and a power on

reset circuit. Internal pull-up resistors are provided for

the TCK, TDI and TMS pins.

The TAP engine is a 16 state FSM, driven by the Test

Clock (TCK) and the Test Mode Select (TMS) pins. An

independent power on reset circuit is provided to ensure

the FSM is in the TEST_LOGIC_RESET state at

power up.

In addition to the minimum IEEE 1149.1 instruction re-

quirements (EXTEST, SAMPLE and BYPASS), three

additional instructions (IDCODE, TRI_ST and SET_I/O)

are provided to further ease board level testing. All

unused instruction codes are reserved.

IEEE 1149.1 Supported Instruction Summary

Inst

Selected

Reg

Inst

Name

Description

Data Reg

Mode

Code

EXTEST External Test

BSR

Test

0000

ID Code

ID Code Inspection

ID Reg

Normal

0001

Sample

Sample Boundary

BSR

Normal

0010

TRI_ST

Force Tristate

Bypass

Normal

0011

SET_I/0 Control Boundary To I/0

Bypass

Test

0100

Bypass

Bypass Scan

Bypass

Normal

1111

After hardware or software reset, the IDCODE instruc-

tion is always invoked. The decoding logic provides sig-

nals to control the data flow in the DATA registers

according to the current instruction.

Each Boundary Scan Register (BSR) cell also has two

stages. A flip-flop and a latch are used in the SERIAL

SHIFT STAGE and the PARALLEL OUTPUT STAGE

respectively.

There are four possible operational modes in the BSR

cell:

(1) CAPTURE

(2) SHIFT

(3) UPDATE

(4) SYSTEM FUNCTION

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