B&B Electronics 232SDD16 manual Bit Assignments for I/O Lines, Read I/O Lines Command

A byte represents an eight-bit binary number (11111111), therefore each byte can represent eight I/O lines. Each bit is assigned a bit position and a weight (value). Refer to Table 3.3.

Table 3.3 - Bit Assignments for I/O Lines

				MOST SIGNIFICANT I/O BYTE
I/O Line #	15	14	13		12	11	10	9	8
Bit Position	7	6	5		4	3	2	1	0
Hex Weight	80	40	20		10	8	4	2	1
Dec. Weight	128	64	32		16	8	4	2	1
				LEAST SIGNIFICANT I/O BYTE
I/O Line #	7	6	5		4	3	2	1	0
Bit Position	7	6	5		4	3	2	1	0
Hex Weight	80	40	20		10	8	4	2	1
Dec. Weight	128	64	32		16	8	4	2	1

To set an output to a HIGH state the corresponding bit position must be set to a "1". Conversely to set an output LOW the corresponding bit position must be set to a "0". When reading I/O lines, any bit set to a "0" indicates the corresponding I/O line is in the LOW state and any bit set to a "1" indicates the corresponding I/O line is in the HIGH state.

Example 3.1 - To set outputs 15, 8, 1, and 0 to a HIGH state, and all other outputs to a LOW state (shown in bold face) -

	MS Byte		LS Byte
Shown in binary -	10000001	00000011
Shown in decimal -	129	3
	(128+1)	(2+1)
Shown in hexadecimal -	81	3
	(80h+1h)		(2h+1h)

Example 3.2 - Reply from Read I/O command (shown in bold face) -

	MS Byte		LS Byte
Shown in binary -	11001000	01010010
Shown in decimal -	200	82
	(128+64+8)	(64+16+2)
Shown in hexadecimal -	C8	52
	(80h+40h+8h)		(40h+10h+2h)

I/O lines #15, 14, 11, 6, 4, 1 are HIGH. All other I/O lines are LOW.

232SDD16-1005 Manual 11

Read I/O Lines Command

The Read I/O Lines command returns two data bytes that reflect the state of the I/O lines. The first data byte contains the most significant I/O lines (15 - 8). The second data byte contains the least significant I/O lines (7 - 0). If a bit is a "0" then the state of that I/O line is LOW. If a bit is a "1" then the state of that I/O line is HIGH.

Command: !0RD

Argument: none

Response: the state of the 16 I/O lines in two 8 bit bytes (shown in bold face)

ASCII Example: !0RDÈR

Dec. Example: !0RD<200><82>

Hex. Example: !0RD<C8><52>

Bin. Example: !0RD<11001000><01010010>

Description: the first byte indicates that I/O lines #15, 14, & 11 are HIGH and I/O lines # 13, 12, 10, 9, & 8 are LOW; the second byte indicates that I/O lines # 6, 4, & 1 are HIGH and I/O lines # 7, 5, 3, 2, & 0 are LOW.

Set Output Lines Command

The Set Output Lines command is used to set the states of the output lines. This command requires two data bytes. These data bytes specify the output state of each output line. The first data byte represents the most significant I/O lines (15 - 8). The second data byte represents the least significant I/O lines (7 - 0). If a bit position is set to a "0" then the state of that output line will be set LOW. If a bit position is set to a "1" then the state of that output line will be set HIGH.

NOTE: Refer to the "Define I/O Lines" command to define an I/O line as an output.

12 232SDD16-1005 Manual

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