American Magnetics 420 Power Supply Programmer - Manual (Page 92)

74 Rev. 7
Remote Interface Reference
Command Handshaking
4.2.4 Command Handshaking
The Model 420 provides an internal command queue that can store up to 4
commands or queries. However, it is possible that the host computer can
overwhelm the command queue by sending commands faster than the
Model 420 can execute. If the Model 420 cannot process a command due to
a full command queue, the command is ignored and the
-303,"Input
overflow" error is reported.
Handshaking is generally not a concern unless more than 4 commands are
sent sequentially. If a query is sent, the user will normally wait for return
data for the queries before proceeding to send the next query or command.
In the case of sending numerous commands in sequence, there are two
methods available to help prevent command queue overflows which are
discussed below.
4.2.4.1 Using the *OPC Command
The *OPC command is executed within the normal command queue. Upon
completed execution of the *OPC command, the “Operation Complete” bit
(bit 0) of the Standard Event register will be set.
Table 4-2. Bit definitions for the Standard Event register.
Bit Number
Decimal
Value Definition
0 Operation Complete 1 All commands prior to and including
*OPC have been executed.
1 Not Used 2 Always “0”.
2 Query Error 4 A query error occurred. See the
error messages in the -200 range.
3 Device Error 8 A device error occurred. See the
error messages in the -400 range.
4 Execution Error 16 An execution error occurred. See the
error messages in the -300 range.
5 Command Error 32 A command error occurred. See the
error messages in the -100 range.
6 Not Used 64 Always “0”.
7 Power On 128 Power has been cycled since the
last time the Standard Event register
was read or cleared.