AM8530H AMD [Advanced Micro Devices], AM8530H Datasheet - Page 110

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

AMD
5.6.1
Local loopback is selected when bit D4 of WR14 is set to ‘1’. In this mode the output of
the transmitter is internally connected to the input of the receiver. At the same time the
TxD pin remains connected to the transmitter. In this mode the DCD pin is ignored as a
receiver enable and the CTS pin is ignored as a transmitter enable even if the Auto En-
ables mode has been selected. Note that the DPLL input is connected to the RxD pin, not
to the input of the receiver. This precludes the use of the DPLL in Local Loopback. Local
Loopback is shown schematically in Figure 5–10.
5.6.2
Auto Echo is selected when bit D3 of WR14 is set to ‘1’. In this mode the TxD pin is con-
nected directly to the RxD pin, and the receiver input is connected to the RxD pin. In this
mode the CTS pin is ignored as a transmitter enable and the output of the transmitter
does not connect to anything. If both the Local Loopback and Auto Echo bits are set to
‘1’, the Auto Echo mode will be selected, but both the CTS pin and the DCD pin will be
ignored as auto enables. This, however, should not be considered a normal operating
mode. Auto Echo is shown schematically in Figure 5–11.
5–16
DCD
DCD
CTS
CTS
Local Loopback
Auto Echo
RxD
RxD
TxD
TxD
Figure 5–10. Local Loopback
N.C.
Figure 5–11. Auto Echo
Local Loopback
Auto Echo
N.C.
RX Enable
RX Enable
TX Enable
TX Enable
Support Circuitry Programming
Transmitter
Transmitter
Receiver
Receiver