REGISTERS AND RAM

13.1 Address Register (Port x5h)

The main register is the ADDRESS Register located at Port x5h. The bit designations are as follows:

Bit

Name

Read/

Write

Description

6-0

Address

Pointer

Read/Write

Address of RAM and Registers. See the tables below for detail.

7

Busy

Read

Only

A one indicates the device is busy because of a Serial Bus transaction or another ISA

bus transaction. With checking this bit, multiple ISA drivers can use LM79 without

interfering with each other or a Serial Bus driver.

It is the user’s responsibility not to have a Serial Bus and ISA bus operations at the

same time.

This bit is:

Set: with a write to Port x5h or when a Serial Bus transaction is in progress.

Reset: with a write or read from Port x6h if it is set by a write to Port x5h, or when the

Serial Bus transaction is finished.

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Busy

Address Pointer (Power On default 00h)

(Power On default 0)

A6

A5

A4

A3

A2

A1

A0

Address Pointer Index (A6–A0)

Registers and RAM

A6–A0 in

Hex

Power On Value of

Registers:

Notes

Configuration Register

40h

0000 1000

Interrupt Status Register 1

41h

0000 0000

Auto-increment to the address of Interrupt

Status Register 2 after a read or write to

Port x6h.

Interrupt Status Register 2

42h

0000 0000

SMI Mask Register 1

43h

0000 0000

Auto-increment to the address of SMI Mask

Register 2 after a read or write to Port x6h.

SMI Mask Register 2

44h

0000 0000

NMI Mask Register 1

45h

0000 0000

Auto-increment to the address of NMI Mask

Register 2 after a read or write to Port x6h.

NMI Mask Register 2

46h

0100 0000

VID/Fan Divisor Register

47h

Serial Bus Address Register

48h

0010 1101

Chip Reset/VID4/Device ID

Register

49h

D7 identifies this device as the LM79. D0

reflects the state of VID4.

POST RAM

00–1Fh

Auto-increment to the next location after a

read or write to Port x6h and stop at 1Fh.

Value RAM

20–3Fh

Value RAM

60–7Fh

Auto-increment to the next location after a

read or write to Port x6h and stop at 7Fh.

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