Real-Time Clock/Complementary Metal Oxide; Semiconductor (Rt/Cmos) Ram Information; Semiconductor (Rt /Cmos) Ram Information; Real-Time Clock Information - IBM 5170 Technical Reference

Real-time Clock/Complementary Metal Oxide
Semiconductor (RT/CMOS) RAM
Information
The RT/CMOS RAM chip (Motorola MC146818) contains the
real-time clock and 64 bytes of CMOS RAM. The internal clock
circuitry uses 14 bytes of this RAM, and the rest is allocated to
configuration information. The following figure shows the CMOS
RAM addresses.
Addresses Description
00-00
*
Real-time clock information
OE
*
Diagnostic status byte
OF
• Shutdown status byte
10 Diskette drive type byte - drives A and B
11
Reserved
12
Fixed disk type byte - drives C and 0
13 Reserved
14 Equipment byte
15 Low base memory byte
16 High base memory byte
17 Low expansion memory byte
18 High expansion memory byte
19-20
Reserved
2E-2F
2-byte CMOS checksum
30
• Low expansion memory byte
31 • High expansion memory byte
32
*
Date century byte
33
*
Information flags (set during power on)
34-3F
Reserved
CMOS RAM Address Map
*
These bytes are not included in the checksum calculation and
are not part of the configuration record.
Real-time Clock Information
The following figure describes real-time clock bytes and specifies
their addresses.
System Board 1-45