AM8530H AMD [Advanced Micro Devices], AM8530H Datasheet - Page 135

• Manufacturer Part Number: AM8530H
• Description: Serial Communications Controller
• Manufacturer: AMD [Advanced Micro Devices]

Register Description
Bits 4 and 3: Transmit Clock 1 and 0
These bits determine the source of the transmit clock as shown in Table 6–7. They do not
interfere with any of the modes of operation of the SCC but simply control a multiplexer
just before the internal transmit clock input. The DPLL output that may be used to feed
the transmitter in FM modes lags by 90 the output of the DPLL used by the receiver. This
makes the received and transmitted bit cells occur simultaneously, neglecting delays. A
hardware reset selects the TRxC pin as the source of the transmit clocks.
Bit 2: TRxC O/I
This bit determines the direction of the TRxC pin. If this it is set to ‘1’, the TRxC pin is an
output and carries the signal selected by D1 and D0 of this register. However, if either the
receive or the transmit clock is programmed to come from the TRxC pin, TRxC will be an
input, regardless of the state of this bit. The TRxC pin is also an input if this bit is set to
‘0’. A hardware reset forces this bit to ‘0’.
Bits 1 and 0: TRxC Output Source 1 And 0
These bits determine the signal to be echoed out of the SCC via the TRxC pin. No signal
is produced if TRxC has been programmed as the source of either the receive or the
transmit clock. If TRxC O/I (bit 2) is set to ‘0’, these bits are ignored.
If the XTAL oscillator output is programmed to be echoed, and the XTAL oscillator has
not been enabled, the TRxC pin hoes High. The DPLL signal that is echoed is the DPLL
signal used by the receiver. Hardware reset selects the XTAL oscillator as the output
source.
Table 6–8. Transmit External Control Selection
D
D
0
0
1
1
0
0
1
1
4
1
Table 6–7. Transmit Clock Source
D
D
0
1
0
1
0
1
0
1
3
0
Transmit Clock = RTxC pin
Transmit Clock = TRxC pin
Transmit Clock = BRG output
Transmit Clock = DPLL output
TRxC = XTAL oscillator output
TRxC = Transmit Clock
TRxC = BRG output
TRxC = DPLL output
AMD
6–25