Manual
3-20 BHK-1/2-MG 121313
originator (computer) and the BHK-MG 40W Power Supply, thus avoiding a more complex
“handshake” protocol.
When the BHK-MG is in the RS 232 echo mode it returns all data sent to the host controller. The
BHK-MG provides two additional options that allow handshake communication: the Prompt
method and the XON XOFF method. In standard echo mode the controller must verify that each
character is echoed back by the BHK-MG. As shown in Figure 3-3, there are times when the
BHK-MG does not echo back the character from the controller, requiring that the controller
resend the character. By using the handshake options (prompt and XON XOFF) the host con-
troller can ensure that serial data interrupts occurring after parsing of the incoming message do
not result in lost data.
Figure 3-3 illustrates the default echo mode, the prompt method and the XON XOFF method
described in the following paragraphs.
FIGURE 3-3. RS 232 IMPLEMENTATION
Only three control characters (characters between 00
H
and 1F
H
) are acknowledged by the
power supply:
• Carriage Return (CR, 0D
H
)
• Line Feed (LF, 0A
H
)
• Back Space (BS, 08
H
)
BS deletes the last character entered, with the exception of CR or LF characters. Either the CR
or LF character acts as the line terminator, initiating parsing of the ASCII data sent to the BHK-
MG by the command originator. When the line is parsed, the BHK-MG sends the line terminator
sequence CR LF to the command originator.
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 3-3).
3.5.3.1 ECHO MODE
Echo mode is the default method of ensuring data is transferred without errors. Each byte (char-
acter) is echoed back to the sender where it is verified as the same character that was just sent.
If the character is incorrect or missing, the sender sends the character again until the correct
character is verified as having been received.
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 3-3).