Omega Engineering DAQ-12 user manual Digital Input/Output, Base Address

2.3Digital Input/Output

The DAQ-12 offers four bits of digital output and four bits of digital input for control/monitoring of external digital devices. The four digital output lines are LS TTL compatible and will initialize low (0 volts) on power-up. The four digital inputs are also LS TTL compatible. There is no termination provided on the digital input lines and a read of an unused digital input will result in an indeterminate value.

2.4Base Address

The DAQ-12 uses 16 consecutive I/O address locations in the range 0 to 0FFFFH. Two six-position switches (SW1 and SW2) are used to select the base address. SW1 controls address lines A15 - A10, and SW2 controls A9 - A4. Address lines A3 - A0 are used internally by the DAQ-12 to select which register to access. When selecting a base address for the DAQ-12, an address selection switch in the "OFF" position corresponds to an address bit of "1" while a switch in the "ON" position corresponds to an address bit of "0". The base address of the DAQ-12 must be set on a 16 byte boundary, meaning A3 - A0 are "0". The address of the DAQ-12 as shipped from the factory is 0300H. This setting and other examples are shown in the Figure 2-5.

	x		x		x		x		x		x
O	1	2		3		4		5		6
N

A A A A A A 15 14 13 12 11 10

SW1

SW2

	x	x		x		x		x		x
O	1	2	3		4		5		6
N

A A A A A A 9 8 7 6 5 4

0000			xxxx	Hex
		0000 : 0
	Bit=0 Bit=1	0001 : 1
		0010 : 2
		0011 : 3
		0100 : 4

		0			3					0
0	0	0	0	0	0	1	1	0	0	0	0

O 1 2 3 4 5 6	O 1 2 3 4 5 6
N	N

Example1:				Base I/O Address = 0300H
		6				A					D
0	1	1	0	1	0		1	0	1	1	0	1
O 1 2		3	4	5 6			O 1	2	3 4		5 6
N							N

00101 : 5

0110 : 6

0111 : 7

1000 : 8

1001 : 9

1010 : A

1011 : B

1100 : C

01101 : D

1110 : E

1111 : F

Example 2: Base I/O Address = 6AD0H

Figure 2-5. I/O Base Address Selection

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