Scc Configuration Register (Scon) - Motorola MC68302 User Manual

• Data Clocked by the Baud Rate Generator or Directly by an External Clock
• Supports Modem Signals (RXD, TXD, RCLK, TCLK, RTS, CTS, and CD)
• Full-Duplex Operation
• Echo Mode
• Local Loopback Mode
4.5.2 SCC Configuration Register (SCON)
4-20
Each SCC controller has a configuration register that controls its operation
and selects its clock source and baud rate. Figure 4-6 shows one of the three
SCC baud rate generators. Each SCON is a 16-bit, memory-mapped, read-
write register. The SCONS are set to $0004 by reset, resulting in the baud
rate generator output clock rate being set to the main clock rate divided by
4.
15 14 13 12 11 10
WOMS EXTC TCS RCS C010 C09 COB COJ CD6 C05 C04 C03 C02 COl COO OIV4
WOMS ---:- Wired-OR Mode Select
When WOMS is set, the TXD driver is programmed to function as an open-
drain output and may be externally wired together with other TXD pins in
an appropriate bus configuration. In this case, an external pullup resistor
is required. When WOMS is cleared, the TXD pin operates normally with
an active internal pullup.
NOTE
This bit is valid only in NMSI mode.
EXTC - External Clock Source
The EXTC bit selects whether the baud rate generator clock source is the
internal main clock (EXTC
=
0) or external clock (EXTC
=
1 ). If EXTC
=
1, the
external clock is taken from the TIN1 pin. Note that the single TIN1 pin can
be used to supply a clock for all three baud rate generators.
TCS - Transmit Clock Source
The TCS bit selects either the baud rate generator output (TCS
=
0) or the
external clock source on the TCLK pin (TCS
=
1) for the transmitter. If TCS
=
0,
then the baud rate generator output is driven onto the TCLK pin.
After reset, TCLK defaults to an input and stays an input until a zero is
written to TCS.
MC68302 USER'S MANUAL MOTOROLA