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CHAPTER 4
Using terminal commands
47
APPLIES TO A720B and A723, but see also the comments in “Remote” on
page 49.
DESCRIPTION A complex command acting upon the I/O ports of a device.
PARAMETERS A control byte specifying the command, the bit of the port the
command is acting on, and two 16-bit parameters, depending on
the control byte; for some commands, one or both of them may be
missing. However, if they are needed for a certain command but
not given, null values are implied.
The control byte’s significance is shown in Figure 14.
Figure 14. Control Byte Layout
• The Port Number selects a the port that will be affected by
the command. For the A720/A723, only 0000 and 0001 are
accepted.
• The Command Code specifies the operation that will be
applied to the selected port.
Table 5 shows the command codes definitions.
Command Code
Port Number
Table 5. Command Code Definitions
Code Description Parameters Returns
0000 RDP – Read Data Port. This command reads the
whole 16-bit port and returns its value; the Port
Number has no significance for this command.
None A 16-bit integer and the
result (OK or ERROR).
0001 RDDR – Read Data Direction Register. This com-
mand reads the whole 16-bit Data Direction
Register and returns its value; the Port Number
has no significance for this command.
None A 16-bit integer and the
result (OK or ERROR).
0010 CAI – Configure the port specified by Port Num-
ber as input (acts upon the Data Direction Regis-
ter).
The port number. Result (OK or ERROR).
0011 CAO – Configure the port specified by Port
Number as output (acts upon the Data Direction
Register).
The port number. Result (OK or ERROR).