IBM 770 manual NMI Mask Register Hex, Bits, 0071, System Board, Data

RT/CMOS	Address and		NMI Mask Register (Hex 0070)
The	NMI	mask	register	is used	with	the RT/CMOS	data register (hex
0071)	to	read	from and	write	to the	RT/CMOS RAM	bytes.

Attention

The operation following a write to hex 0070 should access hex 0071;

otherwise,

intermittent

failures

of

the RT/CMOS RAM

can

occur.

Bit

Function

7

NMI

mask

6–0

RT/CMOS

RAM

address

Figure

2-13. RT/CMOS

Address

and

NMI

Mask

Register

(Hex

0070)

Bit 7

When this write-only bit is set to 1, the NMI is masked

(disabled). This bit is set

to

1

by

a

power-on reset.

Bits

6–0

These

bits

are

used

to

select

RT/CMOS

RAM

addresses.

RT/CMOS

Data

Register

(Hex

0071)

The

RT/CMOS

data

register

is

used

with the RT/CMOS address and

NMI

mask

register

(hex

0070)

to

read

from

and

write

to the

RT/CMOS

RAM

bytes.

Bit

Function

7–0

RT/CMOS

data

Figure 2-14. RT/CMOS Data Register (Hex 0071)

2-20 System Board