IBM 600 manual Status Register Hex 00B, This Bit Indicates Whether Binary-coded-decimal

Status Register	B (Hex	00B)
Bit	Function
7	Set
6	Enable	periodic interrupt
5	Enable	alarm interrupt
4	Enable update-ended interrupt
3	Enable	square wave
2	Date	mode
1	24-hour mode
0	Enable	daylight-saving time

Figure

2-18. Status

Register

B

(Hex

00B)

Bit

7

If

set

to

0,

this

bit

updates

the

cycle,

normally

by

advancing

the count

at

a

rate

of

one

cycle

per

second. If

set to 1, it immediately ends any update cycle in

progress, and the program can initialize the

14

time

bytes

without

any

further

updates

occurring

until

this bit

is set

to

0.

Bit

6

This

is

a

read/write

bit that

allows

an

interrupt

to

occur at

a rate specified by the rate and divider bits in status

register

A. If set to 1, this bit enables

the

interrupt. The

system

initializes

this

bit

to

0.

Bit

5

If

set

to 1, this bit enables the

alarm

interrupt. The

system

initializes

this

bit

to

0.

Bit

4

If

set

to

1,

this

bit

enables

the

update-ended

interrupt.

The

system

initializes

this

bit

to

0.

Bit

3

If

set

to

1,

this

bit

enables

the

square-wave frequency as

set

by

the rate-selection bits in status register A. The

system

initializes

this

bit

to

0.

Bit

2

This

bit

indicates

whether

the

binary-coded-decimal

(BCD)

or binary format is used for time-and-date calendar

updates. If set to 1, this bit indicates binary

format. The

system

initializes

this

bit

to 0.

Bit

1

This

bit

indicates

whether

the

hours

byte is in 12-hour or

24-hour

mode. If set to 1, this bit

indicates the 24-hour

mode. The system

initializes

this

bit

to

1.

Bit

0

If

set

to

1,

this

bit

enables

the

daylight-saving-time mode.

If

set

to

0,

this

bit

disables

the

daylight-saving-time mode,

and the clock reverts to standard time. The system

initializes

this

bit

to

0.

2-22

System Board