HMC Electronics MDL Series BK Precision DC Electronic Load System Module User Manual
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RS-232 Flow Control
The RS-232 interface supports the following flow control options. For each case, the electronic load
will send a maximum of five characters after hold-off is asserted by the controller. The electronic
load is capable of receiving as many as fifteen additional characters after it asserts hold-off.
CTS/RTS: The electronic load asserts its Request to Send (RTS) line to signal hold-off when
its input buffer is almost full, and it interprets its Clear to Send (CTS) line as a hold-off signal
from the controller.
XON/XOFF: When the input queue of the electronic load becomes more than ¾ full, the
instrument issues an X-OFF command. The control program should respond to this and stop
sending characters until the electronic load issues the X-ON, which it will do once its input
buffer has dropped below half-full. The electronic load recognizes X_ON and X_OFF sent
from the controller. An X-OFF will cause the electronic load to stop outputting characters
until it sees an X-ON.
NONE: No flow control.
Flow control options are stored in non-volatile memory.
RS-232 Connections
The RS-232 serial port can be connected to the serial port of a controller (i.e., personal computer)
using a straight-through RS-232 cable terminated with DB-9 connectors. Do not use a null modem
cable. Figure 33 shows the pinout for the connector.
If your computer uses a DB-25 connector for the RS-232 interface, you will need a cable or adapter
with a DB-25 connector on one end and a DB-9 connector on the other. It must be a straight-
through (not null modem) cable.
Figure 33 - RS-232 Connector Pinout
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