w65c51n Western Design Center, Inc., w65c51n Datasheet - Page 14

• Manufacturer Part Number: w65c51n
• Description: Asynchronous Communications Interface Adapter Acia
• Manufacturer: Western Design Center, Inc.

ACIA/MODEM INTERFACE
Crystal Pins (XTLI, XTLO)
These pins are normally directly connected to the external crystal (1.8432 MHz) to derive the various
baud rates. Alternatively, an externally generated clock can drive the XTLI pin, in which case the XTLO
pin must float. XTLI is the input pin for the transmit clock.
Transmit Data (TxD)
The TxD output line transfers serial non-return-to-zero (NRZ) data to the modem. The least significant bit
(LSB) of the Transmit Data Register is the first data bit transmitted and the rate of data transmission is
determined by the baud rate selected or under control of an external clock. This selection is made by
programming the Control Register.
Receive Data (RxD)
The RxD input line transfers serial NRZ data into the ACIA from the modem, LSB first. The receiver data
rate is either the programmed baud rate or under the control of an externally generated receiver clock.
The selection is made by programming the Control Register.
Receive Clock (RxC)
The RxC is a bi-directional pin which is either the receiver 16x clock input or the receiver 16x clock output.
The latter mode results if the internal baud rate generator is selected for receiver data clocking.
Request to Send (RTSB)
The RTSB output pin controls the modem from the processor. The state of the RTSB pin is determined
by the contents of the Command Register.
Clear to Send (CTSB)
The CTSB input pin controls the transmitter operation.
The enable state is with CTSB low.
The
transmitter is automatically disabled if CTSB is high.
Data Terminal Ready (DTRB)
This output pin indicates the status of the ACIA to the modem. A low on DTRB indicates the ACIA is
enabled, a high indicates it is disabled. The processor controls this pin via bit 0 of the Command
Register.
Data Set Ready (DSRB)
The DSRB input pin indicates to the ACIA the status of the modem. A low indicates the “ready” state and
a high, “not-ready”
Data Carrier Detect (DCDB)
The DCDB input pin indicates to the ACIA the status of the carrier-detect output of the modem. A low
indicates that the modem carrier signal is present and a high that it is not.
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