Support Circuitry Programming
AMD
5–4
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
0
0
0
1
1
0
1
1
0
0
0
1
1
0
1
1
0
0
0
1
1
0
1
1
TRxC
Out = XTAL Output
TRxC
Out = Transmit Clock
TRxC
Out = BR Generator Output
TRxC
Out = DPLL Output
TRxC
O/I
Transmit Clock =
RTxC
Pin
Transmit Clock =
TRxC
Pin
Transmit Clock = BR Generator Output
Transmit Clock = DPLL Output
Receive Clock =
RTxC
Pin
Receive Clock =
TRxC
Pin
Receive Clock = BR Generator Output
Receive Clock = DPLL Output
RTxC
X TAL/
NO
X TAL
WR11—Clock Mode Control
5.2.2
The source of the receive clock is controlled by bits D6 and D5 of WR11. The receive
clock may be programmed to come from the
RTxC
pin, the
TRxC
pin, the output of the
baud rate generator, or the transmit output of the DPLL.
Rec eive Cloc k S ourc e
5.2.3
The source of the transmit clock is controlled by bits D4 and D3 of WR11. The transmit
clock may be programmed to come from the
RTxC
pin, the
TRxC
pin, the output of the
baud rate generator, or the transmit output of the DPLL.
T ransmit Cloc k S ourc e
Ordinarily the
TRxC
pin is an input, but it becomes an output if this pin is not selected as
the source for the transmitter or the receiver, and bit D2 of WR11 is set to ‘1’. The selec-
tion of the signal provided on the
TRxC
output pin is controlled by bits D1 and D0 of
WR11. The
TRxC
pin may be programmed to provide the output of the crystal oscillator,
the output of the BRG, the receive output of the DPLL or the actual transmit clock. If the
output of the crystal oscillator is selected but the crystal oscillator has not been enabled,
the
TRxC
pin will be driven High. The option of placing the transmit clock signal on the
TRxC
pin, when it is an output, allows access to the transmit output of the DPLL.