Verilink AS56/56Plus (896-502588-001) Product Manual - Manual (Page 108)

Auxiliary Ports
6-30 AS56 and AS56 Plus User Manual
Printer Port Flow Control
The unit’s port supports simultaneous hardware and software flow control
signaling from the attached device. The hardware control is RTS if
connected directly to a printer or CD if connected via a modem. The
software control is XOFF/XON. The XOFF is DC-3 (
CNTL - S ); however,
any character arriving at the port is treated as an XON (to protect against
a damaged DC-1).
Hardware control has priority; if RTS (or CD) is low, transmission to the
device will be suspended and the data will be buffered in the AS56.
Receipt of software flow control characters while RTS (or CD) is low will
have no effect on the port. Transmission will be resumed when RTS (or
CD) goes high.
If the port receives an XOFF while RTS (or CD) is high, transmission will
be suspended and the data will be buffered. Transmission will be resumed
if any subsequent character (including another XOFF) is received OR if
RTS (or CD) is lowered and subsequently raised. This mechanism
protects against a “lost” XON.