5.2.2 Using an External Clock Signal (TIP867-20R only)
The TIP867 can be programmed to receive an external clock signal or transmit an external clock
signal. For both modes the SCCs TRxC# pin is used as clock I/O pin (programmable as clock input or
clock output).
For proper use of the external clock, both the clock signal transceiver direction and the SCC TRxC#
pin I/O direction must be configured properly. The RS485 clock transceiver direction is controlled by
the SCCs DTR pin, used as general purpose output.
For using the SCCs DTR pin as a general purpose output, bit D2 in the SCC internal WR14 register
must be set to ‘0’.
After hardware reset both the clock signal transceiver and the TRxC# pin are configured as
input for all channels.
5.2.2.1 Receiving an external clock signal
To use the SCCs TRxC# pin as an input for an external clock, first the TRxC# pin direction must be set
to input, and then the clock signal receiver must be enabled.
To enable the clock receiver, bit D7 of the Z85230 internal WR5 register must be set to ‘0’.
To program the SCCs TRxC# pin as clock input, bit D2 of the SCC internal WR11 register must be set
to ‘0’. The external clock is used as transmit clock if the bits D[4:3] of the SCC internal WR11 register
are set to ‘01’ and it is used as receive clock if the bits D[6:5] are set to ‘01’.
5.2.2.2 Transmitting an external clock signal
To use the SCCs TRxC# pin as an output for an external clock, first the clock signal transmitter must
be enabled, and then the TRxC# pin I/O direction must be set to output.
To enable the clock transmitter, bit D7 of the SCC internal WR5 register must be set to ‘1’.
To program the SCCs TRxC# pin as clock output, bit D2 of the SCC internal WR11 register must be
set to ‘1’. The source of the external clock is selected by the state of the bits D[1:0] of the SCC internal
WR11 register.
D[1:0]
Clock Source
‘00’
7.3728 MHz Oscillator
‘01’
Transmit Clock
‘10’
Baud Rate Generator Output
‘11’
DPPL Output
Table 5-1 : External Clock Sources
TIP867 User Manual Issue 1.0.5
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