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2.4.1 The 8254 Counter
The 8254 Programmable timer/counter has 4 registers from Base+0 through
Base+3. For detailed programming information about the 8254, please refer
to Intel‘s “Microsystem Components Handbook”.
Address Read Write
Base+0 8254 Counter 0 8254 Counter 0
Base+1 8254 Counter 1 8254 Counter 1
Base+2 8254 Counter 2 8254 Counter 2
Base+3 Reserved 8254 Counter Control
2.4.2 A/D Input Buffer Register
(READ) Base+4: A/D Low Byte Data Format
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
D7 D6 D5 D4 D3 D2 D1 D0
(READ) Base+5: A/D High Byte Data Format
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
0 0 0 READY D11 D10 D9 D8
A/D 12 bit data: D11…..D0, D11 = MSB, D0 = LSB
READY = 1: A/D 12 bits data not ready
= 0: A/D 12 bits data is ready
The low 8 bits of A/D data are stored in address BASE+4 and the high 4 bits of data are
stored in address BASE+5. The READY bit is used as an indicator for A/D conversion.
When a A/D conversion is completed, the READY bit will be cleared to zero (Low).
OME-A-8111 Hardware Manual (ver.1.1, Jul/2003) 12