Dynapro Technologies Dynapro ET TCS, Application Developer'S Manual

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2-12
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When the TCS address is changed from RS232 or RS485 to a multidrop address and the host
has been stalled.
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The TCS address is changed to RS232 or RS485, the TCS was not addressed for two-way
communication, and the input buffer is less than 75% full.
When XON/XOFF mode is on, the user can manually unstall the host by pressing Ctrl/Q on the
optional keyboard, as long as the host is not in a stall condition as a result of a filled TCS input
buffer. If the host is stalled for this reason, pressing Ctrl/Q will not override the stall. Refer to
XON/XOFF Mode Command in Chapter 4 for a full description of how TCS handles Ctrl/Q
keystrokes.
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When XON/XOFF mode is on, the host can stall the TCS by turning the CTS line off, or by
sending an XOFF code, or both. When XON/XOFF mode is off, the host stalls the TCS by
turning the CTS line off. To improve performance, the TCS uses a two character transmit buffer.
Upon receiving a stall signal from the host, the TCS stops all transmissions when the two-
character transmit buffer is emptied. In some situations, the host is unable to accept more than
one character when the stall signal is sent. Under these conditions, the TCS can be configured in
Setup to use a single character transmit buffer which would result in transmissions stopping on
the next code boundary after the stall signal was received.
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How the host unstalls the TCS depends on how the TCS was stalled. If the host stalled the TCS
by switching the CTS line off, it unstalls the TCS by switching CTS on. If the host stalled the
TCS by sending an XOFF code, it must send an XON mode to unstall the TCS. Note that TCS
ignores XON and XOFF codes when XON/XOFF mode is disabled.