Section 2, The 8254 registers, The di / do register – Omega 1002 User Manual
Page 30: The a/d buffer, 2 the di / do register, 3 the a/d buffer
3.2.2
Section 2
This group of registers is used by the add-on control logic. 64 bytes of
I/O locations are used. Their detailed descriptions are shown below
3.2.2.1 The 8254 Registers
The 8254, programmable timer/counter, is used to generate periodic
interrupts, A/D trigger and the machine independent timer. Addresses 00h,
04h, 08h and 0Ch are used to program the 8254.
Timer 0 is used as Pacer 0 and timer 1 is used as Pacer 1. Timer 2 is used
as the machine independent timer (P1002_Dealy() function). Refer to Intel’s
“Microsystem Components Handbook” for detailed programming information.
3.2.2.2 The DI / DO Register
Address 20h is used for DI / DO ports. Write to this port to send data to
the DO register. Read from this port to input DI data.
3.2.2.3 The A/D Buffer
Address 30h is used for the A/D buffer. This is a read-only address.
Reading from this port will return the data from A/D buffer. The format of A/D
buffer is:
Bit15-12 Bit11-0
Analog input
channel
A/D data
Bit15-12: The channel number of the analog input. Only lower 4 bits of
channel number are shown in this register.
Bit11-0: The A/D data.
30