xr88c681 Exar Corporation, xr88c681 Datasheet - Page 74

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

In this mode:
1. Received data is transmitted on the channel’s TXD
2. The receiver must be enabled but the transmitter need
3. The channel’s TXRDY and TXEMT status bits are
4. The received parity is checked but is not generated for
5. Character framing is checked but the stop bits are
output.
not be enabled.
inactive.
transmission. Thus, transmitted parity is as received.
transmitted as received.
Rev. 2.11
Incoming
Serial Data
Receive Holding
Register
RXDn
(To be read by the CPU)
Figure 39. A Block Diagram Depict Automatic Echo Mode
Receive Shift Register
To Data Bus
8
RXCn
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6. A received break is echoed as received until the next
7. CPU to receiver communications operates normally,
Each DUART channel can be configured into one of two
diagnostic modes.
Local Loopback Mode
This mode is selected by setting MR2n[7:6] = 10.
Figure 40 is a diagram depicting Local Loopback Mode
operation.
TXCn
valid start bit is detected.
but the CPU to transmitter link is disabled.
Transmit Shift Register
CPU has no access to
the Transmitter
TXDn
Transmit Holding
Register
Outgoing Serial
Data