Operations - IBM AT 5170 Technical Reference

110
Operations
Writing to CMOS RAM involves two steps:
1. OUT to port hex 70 with the CMOS address that will be
written to.
2. OUT to port hex 71 with the data to be written.
Reading CMOS RAM also requires two steps:
1. OUT to port hex 70 with the CMOS address that is to be
read from.
2. IN from port hex 71, and the data read is returned in the AL
register.
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System Board