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5.7
F Option
The F option module allows the model 5902 modem to operate with DTE devices that do not
implement the proper RTS/CTS hardware handshake. This includes most personal computer
SCADA software and many programmable controllers. The F option allows these devices to
communicate over two wire systems, multi-point four wire systems and radios.
The F option module is a data buffer that stores up to 64 characters received from the DTE. The data
buffer provides the RTS/CTS handshake to the modem. When characters have been received into
the buffer, the RTS signal is asserted to request transmission. When the modem asserts the CTS
signal, the characters are transmitted from the buffer.
The F option module continuously asserts the CTS and DSR signals to the DTE. It ignores the RTS
and DTR signals from the DTE. The DCD signal to the DTE follows the state of the CD LED. This
means the DTE can use a three wire RS-232 interface consisting of TxD, RxD and ground. No other
signals are necessary.
The buffer capacity of 64 bytes allows the model 5902 to receive approximately 0.5 seconds of data
transmission from the DTE before the data must be transmitted. Provided the DTE does not transmit
more than 64 characters when the modem is incapable of re-transmitting them (e.g. while the modem
is receiving data), the buffer capacity is adequate for all combinations of RTS/CTS (except 1000
ms), CSH, SCT and CL delays.
All modem configuration switches are fully functional with the option module installed.
5.7.1
Supported Communication Parameters
The F option operates with any of the following word length and parity combinations. Other
combinations are not supported.
8 data bits, no parity
data bits, with parity (even, odd, mark or space)
5902 Bell 202 Modem Hardware Manual
October 19, 2007
37
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