21.1 Data Acquisition Circuit Digital I/O Ports

These 3 ports are called A, B, and C and are accessible on the data acquisition I/O connector J17. Ports A and B can be configured as either input or output, and each half of port C can be configured independently for input or output. The data is read and written with the registers at base+8 through base+10, and the direction configuration byte is located at register Base+11. See the detailed register description in chapter 14 on page 46.

To use these ports, first configure the desired directions by writing the appropriate configuration value to base+11. Then read or write data to the 3 I/O ports as needed. All I/O ports are in input mode on power-up or after a board reset.

The upper 4 bits of port C serve dual purposes. If control bit DIOCTR=0, these bits are normal DIO lines and can be read or written via the register at base+10. If DIOCTR=1, these bits are reassigned as counter/timer signals:

J17 Pin No.	DIOCTR = 1	DIOCTR = 0
21	Gate 0	DIO C4
22	Gate 1	DIO C5
23	Clk 1	DIO C6
24	Out 0	DIO C7

Register Map for Data Acquisition Circuit Digital I/O Ports:

Base +	R/W	7	6	5	4	3	2	1	0
8	R/W	A7	A6	A5	A4	A3	A2	A1	A0
9	R/W	B7	B6	B5	B5	B3	B2	B1	B0
10	R/W	C7	C6	C5	C4	C3	C2	C1	C0
11	R/W	DIOCTR	DAMODE	DASIM	DIRA	DIRCH	-	DIRB	DIRCL

A7-0	Digital I/O port A
B7-0	Digital I/O port B
C7-0	Digital I/O port C
DIOCTR	Se description above and chapter 22 for DIOCTR’s effect on I/O connector J17
DIRA	Port A direction. 0 = output, 1 = input
DIRB	Port B direction. 0 = output, 1 = input
DIRCH	Port C bits 7-4 direction: 0 = output, 1 = input. This bit has no effect if DIOCTR=1.
DIRCL	Port C bits 3-0 direction: 0 = output, 1 = input