IBM TM7 - Manual (Page 48)

DTR Operation: A DTR signal becomes inactive when the system is not ready to
receive data (for example, at power-on reset or when its buffer is full).
XON/XOFF Control
XON Definition: = DC1 (X'11')
XOFF Definition: = DC3 (X'13')
During XON/XOFF control, the printer transmits an XON every 3 seconds after a
power on reset (POR) completes to indicate the printer is ready to receive data.
When the first message is received, the printer stops transmitting the XON signal.
The printer transmits an XOFF when the RS-232 input buffer is 80% full after which
it transmits one XON when the buffer is 20% full.
XON/XOFF Transparent Mode Operation
This is the default mode. See “Message from the Printer” on page 160 for the
format of printer to system messages, which include a byte count, status bytes, and
optional extended status bytes or user data.
XON and XOFF signals are always transmitted independently and are not inside
any part of the message, including the byte count, status bytes, or user data. When
a message includes optional user data, the byte count (bytes 1 and 2) can include
X'10', X'11', or X'13'. When X'10', X'11', or X'13' occur in transparent XON/XOFF
mode, the byte count is bit-exclusive-OR’ed with X'21' and is prefixed by the DLE
(X'10') character to become:
Value in Message Becomes
X'10' X'1031'
X'11' X'1030'
X'13' X'1032'
User data with X'10', X'11', or X'13' is also treated this way in transparent
XON/XOFF mode. The byte count is not incremented for such extra characters.
Determining XON/XOFF Control
You can determine whether XON/XOFF control is being used by sending the
extended address command and checking the feature byte, bit 3. If this bit is set,
the printer is in XON/XOFF mode. (See “Extended Address Command – Request
Printer ID” on page 107.
Disabling XON/XOFF Transparent Mode
You can disable transparent XON/XOFF mode as described in “Real-Time
Requests” on page 156. When disabled, X'10', X'11', or X'13' can occur within
messages. However, because such values are actual count bytes or data bytes and
are not XON or XOFF characters (DLE, XON, and XOFF characters do not occur
within messages), no transform takes place. The values are not bit-exclusive-OR’ed
with X'21' because no transform occurs for such values within messages as it does
during transparent XON/XOFF mode. DLE, XON, or XOFF occur only before or
after a message.
updated March 18, 2002
24 SureMark DBCS User’s Guide