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5.1.2. Communications Port Configuration
The COM port should have the following configuration:
9600 baud
8 data bits
1 stop bit
No parity
This interface does not support XON/XOFF protocol or any hardware
handshaking. The controller should be configured to ignore the handshaking
lines DTR (pin 4), DSR (pin 6) CTS (pin 8) and RTS (pin 7). If the port cannot be
configured through software to ignore these lines the handshake lines should be
jumpered together in two different sets. Pins 4 and 6 should be jumpered
together and pins 7 and 8 should be jumpered together at the controller end of
the cable.
5.1.3. Sending and Receiving Commands
Sending Data
Once a command is sent to the instrument over the USB/RS-232 bus the
instrument will send one of two responses. If the transfer was recognized and
completed the instrument will return with 06 hex or 6 decimal, the Acknowledge
(ACK) ASCII control code. If there is an error with the command string that is
sent, the instrument will respond with 15 hex or 21 decimal, the Not Acknowledge
(NAK) ASCII control code. The ACK or NAK response allows for software
handshaking to monitor and control data flow.
Receiving Data
When requesting data from the instrument it will automatically send the data back
to the controller input buffer. The controller input buffer will accumulate data
being sent from the instrument, including the ACK and NAK response strings,
until it has been read by the controller.
5.2. GPIB Interface
This interface is optional on the SC6540 and provides all of the control
commands and parameter setting commands of the USB/RS-232 interface along
with 488.2 Common Commands and SRQ capability. All commands can be
found in section 5.5. USB/RS-232/GPIB Command List.
Signals and Lines
The GPIB consists of 16 signal lines and 8 ground-return or shield drain lines.
The 16 signal lines are grouped into 8 data lines, 3 handshake lines and 5
interface management lines.
Data Lines: The eight data lines, DI01 through DI08 carry data and command
messages. The 7-bit ASCII or ISO code set is used and the eighth bit DI08 is
unused.
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