AM79C961AVC datasheet(29/206 Pages) AMD

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Am79C961A

SBHE

System Bus High Enable

Input

This signal indicates the HIGH byte of the system data

bus is to be used. There is a weak pull-up resistor on

this pin. If the PCnet-ISA II controller is installed in an

8-bit only system like the PC/XT, SBHE will always be

HIGH and the PCnet-ISA II controller will perform only

8-bit operations. There must be at least one LOW going

edge on this signal before the PCnet-ISA II controller

will perform 16-bit operations.

SD0-15

System Data Bus

Input/Output

This bus is used to transfer data to and from the PC-

net-ISA II controller to system resources via the ISA

data bus. SD0-15 is driven by the PCnet-ISA II

controller when performing slave read operations.

Likewise, the data on SD0-15 is latched by the PC-

net-ISA II controller when performing slave write

operations.

Board Interface

APCS/IRQ15

Address PROM Chip Select

Output

This signal is asserted when the external Address

PROM is read. When an I/O read operation is per-

formed on the first 16 bytes in the PCnet-ISA II

controller’s I/O space, APCS is asserted. The outputs

of the external Address PROM drive the PROM Data

Bus. The PCnet-ISA II controller buffers the contents of

the PROM data bus and drives them on the lower eight

bits of the System Data Bus. IOCS16 is not asserted

during this cycle.

BPAM

Boot PROM Address Match

Input

This pin indicates a Boot PROM access cycle. If no

Boot PROM is installed, this pin has a default value of

HIGH and thus may be left connected to VDD.

BPCS

Boot PROM Chip Select

Output

This signal is asserted when the Boot PROM is read. If

BPAM is active and MEMR is active, the BPCS signal

will be asserted. The outputs of the external Boot

PROM drive the PROM Data Bus. The PCnet-ISA II

controller buffers the contents of the PROM data bus

and drives them on the System Data Bus. IOCS16 is

not asserted during this cycle. If 16-bit cycles are

performed, it is the responsibility of external logic to

assert MEMCS16 signal.

DXCVR/EAR

Disable Transceiver/

External Address Reject

Input/Output

This pin disables the transceiver. The DXCVR output is

configured in the initialization sequence. A high level

indicates the Twisted Pair Interface is active and the

AUI is inactive, or SLEEP mode has been entered. A

low level indicates the AUI is active and the Twisted Pair

interface is inactive.

If EADI mode is selected, this pin becomes the EAR

input.

The incoming frame will be checked against the inter-

nally active address detection mechanisms and the

result of this check will be OR’d with the value on the

EAR pin. The EAR pin is defined as REJECT. (See the

EADI section for details regarding the function and tim-

ing of this signal).

LED0-3

LED Drivers

Output

These pins sink 12 mA each for driving LEDs. Their

meaning is software configurable (see section The ISA

Bus Configuration Registers) and they are active LOW.

When EADI mode is selected, the pins named LED1,

LED2, and LED3 change in function while LED0

continues to indicate 10BASE-T Link Status. The

DXCVR input becomes the EAR input.

PRAB0-15

Private Address Bus

Input/Output

The Private Address Bus is the address bus used to

drive the Address PROM, Remote Boot PROM, and

SRAM.

PRDB3-7

Private Data Bus

Input/Output

This is the data bus for the static RAM, the Boot PROM,

and the Address PROM.

PRDB2/EEDO

Private Data Bus Bit 2/Data Out

Input/Output

A multifunction pin which serves as PRDB2 of the

private data bus and, when ISACSR3 bit 4 is set,

changes to become DATA OUT from the EEPROM.

LED

EADI Function

1SF/BD

2SRD

SRDCLK

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