IBM 770 manual Rt/Cmos Ram, System Board, Address

RT/CMOS RAM

The RT/CMOS RAM (real-time clock/complementary metal-oxide

semiconductor

RAM) module contains the real-time clock

and 128

bytes of CMOS RAM. The clock

circuitry uses 14 bytes of this

memory; the

remainder is allocated to configuration and

system-status

information. A battery is built

into

the module

to keep

the

RT/CMOS

RAM active

when

the

power supply

is not

turned

on.

In

addition

to the 128 bytes of CMOS/RAM, a CMOS/RAM extension

of

4

KB

is

provided

for

configuration

and

other

system information.

Figure 2-12

lists

the

RT/CMOS

RAM

bytes

and

their

addresses.

Address

(Hex)

RT/CMOS

RAM

Bytes

000–00D

Real-time

clock

00E

Diagnostic

status

00F

Shutdown

status

010

Diskette

drive type

011

Hard

disk

2 and

3 drive type

012

Hard disk 0 and 1 drive type

013

Reserved

014

Equipment

015,

016

Low

and

high base memory

017,

018

Low and high expansion memory

019

Hard disk 0 extended byte

01A

Hard disk 1 extended byte

01B

Hard disk 2 extended byte

01C

Hard disk 3 extended byte

01D–02D

Reserved

02E,

02F

Checksum

030,

031

Low

and

high usable memory above 1 MB

032

Date-century

033–07F

Reserved

Figure

2-12. RT/CMOS

RAM

Address

Map

System Board 2-19