xr88c681 Exar Corporation, xr88c681 Datasheet - Page 75

• Manufacturer Part Number: xr88c681
• Description: Cmos Dual Channel Uart Duart
• Manufacturer: Exar Corporation

In this mode:
1. The transmitter output is internally connected to the
2. The transmit clock is used for the receiver.
3. The channel’s TXDn output is held marking (high).
4. The channel’s RXDn input is ignored.
5. The transmitter is enabled, but the received need not
6. CPU to transmitter and receiver communications
RXDn
receiver input.
be enabled.
continue normally.
Rev. 2.11
Receive Holding
Register
Figure 40. A Block Diagram depicting Local Loopback Mode Operation
Receive Shift Register
(To be read by the CPU)
To Data Bus
8
TXCn
75
Remote Loopback Mode.
This mode is selected by setting MR2n[7:6] = 11.
Figure 41 presents a diagram depicting Remote
Loopback Mode operation.
Transmit Shift Register
(Parallel Data from CPU)
From Data Bus.
8
XR88C681
Transmit Holding
Register
V
CC
TXDn