BIT 4886 051010
4-11
All non-control characters are sent via the serial port of the command originator. The control
character BS is echoed as BS Space BS. Only the first control character is returned in response
to either a CR LF or LF CR character sequence (see Figure 4-4).
4.5.2.1
ECHO MODE
Echo mode is one method of ensuring data is transferred without errors. This mode should only
be enabled when errors in operation are detected. Refer to PAR. B.76 to change the setting.
Each byte (character) is echoed back to the sender where it is verified as the same character
that was just sent. If the wrong character is echoed back, sending the ESC character clears the
line to allow retransmission of the character. It is important that CR and LF characters are NOT
sent until the verification process is complete.
When working in echo mode, it is possible to receive the NAK (15 hex) from the BIT 4886. This
indicates an unknown quantity of echoed characters have been lost due to a queue overflow
problem. The error queue will also contain the
-400, QUE error
message, To prevent this,
please insure the received data string does not exceed 127 characters between line terminators
and no more than four queries are sent between line terminators in SCPI mode of operation
All non-control characters are sent via the serial port of the command originator.
4.5.2.2
XON XOFF METHOD
The XON XOFF method allows the BIT 4886 to control when the command originator is allowed
to send data. The command originator can only send data after the XON (transmission on) char-
acter (011
H
) has been received; the command originator stops sending data after receiving the
XOFF (transmission off) character (013
H
), and waits until the XON character is received before
sending additional data. Refer to PAR. B.78 to change the setting.
Control characters, either CR or LF, are returned as XOFF CR if echo mode is on, and as XOFF
if echo mode is off. XOFF stops data from the command originator and the BIT 4886 returns the
normal sequence of CR LF (if echo mode is enabled).
4.5.2.3
ISOLATING RS 232 COMMUNICATION PROBLEMS
A Loop Back test can be executed to aid in isolating RS 232 communication problems. The test
is executed via a SCPI command sent over the GPIB interface.
1. Send the command DIAG:LBT? to the unit via the GPIB interface with the Loop Back Test
connector (Kepco P/N 195-0111) NOT installed. The response sent over the GPIB will be
FAILED
.
2. Install the Loop Back Test connector (Kepco P/N 195-0111) into the RS 232 port; if this con-
nector is not available, skip this step and proceed to step 3. Send DIAG:LBT? again and
read back the answer. if the response is PASSED, the power supply is operating properly. If
the response is FAILED, the unit requires repair.
3. To test the integrity of the cable assembly connecting the BIT 4886 RS 232 port to the com-
puter, remove the Loop Back test connector from the BIT 4886 RS 232 port and connect the
cable in its place. With the DB9 adapter installed on the opposite end of the cable, connect a
short jumper wire between pins 2 and 3 of the adapter connector and repeat the test of step
2 above. If the response is FAILED, the cord is either an improper type (not null modem) or
