IBM 560E manual Bytes, Status, Register A, Bits, Clock

Real-Time

Clock

Bytes

(Hex

000–00D):

Bit

definitions

and

addresses for the real-time

clock

bytes

are

shown

in

Figure 2-15.

Address

(Hex)

Function

Byte

Number

000

Seconds

0

001

Second alarm

1

002

Minutes

2

003

Minute

alarm

3

004

Hours

4

005

Hour

alarm

5

006

Day

of week

6

007

Date

of

month

7

008

Month

8

009

Year

9

00A

Status

register

A

10

00B

Status

register

B

11

00C

Status

register

C

12

00D

Status

register

D

13

Figure

2-15. Real-Time

Clock

Bytes

(Hex

000–00D)

Note:

The

Setup

program

initializes

status

registers

A

and

B when

the time and date are set. Interrupt 1AH is the BIOS

interface to read and set the time and date; it initializes the

registers

in

the

same

way

that the Setup program

does.

Status

Register A

(Hex

00A)

BitFunction

7Update in progress

6–422-stage divider

3–0Rate-selection bits

Figure

2-16. Status

Register

A

(Hex

00A)

Bit

7

When

set

to

1,

this

bit

indicates

that the time-update

cycle

is

in

progress. When set to 0, it indicates

that the

current

date

and

time

can

be

read.

Bits

6–4

These

bits identify which time-base

frequency is

being

used.

The system initializes these bits to binary 010,

which

selects a 32.768-kHz time base. This is the only

value

supported

by

the

system

for proper timekeeping.

Bits

3–0These bits allow the selection of a divider output

frequency. The system

initializes the

rate-selection

bits

to a

binary

0110, which selects a 1.024-kHz

ThinkPad

560/560E System

Board

2-19