IBM 560 - Manual (Page 39)

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.
Figure 2-13. RT/CMOS Address and NMI Mask Register (Hex 0070)
Bit Function
7 NMI mask
6–0 RT/CMOS RAM address
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.
Figure 2-14. RT/CMOS Data Register (Hex 0071)
Bit Function
7–0 RT/CMOS data
ThinkPad 560/560E System Board 2-17