Lenovo ThinkPad 560E TP 560Z Technical Reference Manual - Page 37

RT/CMOS RAM I/O Operations

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RT/CMOS RAM I/O Operations During I/O operations to the RT/CMOS RAM addresses, you should mask interrupts to prevent other interrupt routines from changing the RT/CMOS address register before data is read or written. After I/O operations, you should leave the RT/CMOS address and NMI mask register (X'0070') pointing to status register D (X'00D'). Attention The operation following a write to X'0070' should access X'0071'; otherwise, intermittent failures of the RT/CMOS RAM can occur. Writing to the RT/CMOS RAM requires the following: 1. Write the RT/CMOS RAM address to the RT/CMOS address and NMI mask register (X'0070'). 2. Write the data to the RT/CMOS data register (X'0071'). 3. Write the address, X'0F', to the RT/CMOS and NMI mask register; this leaves X'0070' pointing to the shutdown status byte (X'0F'). 4. Read address X'0071' to restore the RT/CMOS. Reading from the RT/CMOS RAM requires the following steps: 1. Write the RT/CMOS RAM address to the RT/CMOS and NMI mask register (X'0070'). 2. Read the data from the RT/CMOS data register (X'0071'). 3. Write the address, X'0F', to the RT/CMOS and NMI mask register; this leaves X'0070' pointing to the shutdown status byte (X'0F'). 4. Read address X'0071' to restore the RT/CMOS. ThinkPad 560Z System Board 2-19

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RT/CMOS RAM I/O Operations
During I/O operations to the RT/CMOS RAM addresses, you should
mask interrupts to prevent other interrupt routines from changing the
RT/CMOS address register before data is read or written.
After I/O
operations, you should leave the RT/CMOS address and NMI mask
register (X
'
0070
'
) pointing to status register D (X
'
00D
'
).
Attention
The operation following a write to X
'
0070
'
should access
X
'
0071
'
; otherwise, intermittent failures of the RT/CMOS RAM
can occur.
Writing to the RT/CMOS RAM requires the following:
1. Write the RT/CMOS RAM address to the RT/CMOS address and
NMI mask register (X
'
0070
'
).
2. Write the data to the RT/CMOS data register (X
'
0071
'
).
3. Write the address, X
'
0F
'
, to the RT/CMOS and NMI mask
register; this leaves X
'
0070
'
pointing to the shutdown status
byte (X
'
0F
'
).
4. Read address X
'
0071
'
to restore the RT/CMOS.
Reading from the RT/CMOS RAM requires the following steps:
1. Write the RT/CMOS RAM address to the RT/CMOS and NMI
mask register (X
'
0070
'
).
2. Read the data from the RT/CMOS data register (X
'
0071
'
).
3. Write the address, X
'
0F
'
, to the RT/CMOS and NMI mask
register; this leaves X
'
0070
'
pointing to the shutdown status
byte (X
'
0F
'
).
4. Read address X
'
0071
'
to restore the RT/CMOS.
ThinkPad 560Z System Board
2-19