xr88c681 Exar Corporation, xr88c681 Datasheet - Page 73

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

MR2n[7:6] - Channel Mode Select
Each Channel can operate in one of four modes.
D Setting MR2n[7:6] = 00 configures the channel to op-
erate in the Normal Mode. In this mode, the receiver
and transmitter operate independently.
presents a diagram depicting Normal Mode Opera-
tion.
Rev. 2.11
Incoming
Serial Data
Receive Holding
Register
RXDn
(To be read by the CPU)
Receive Shift Register
Figure 38. A Block Diagram Depicting Normal Mode Operation.
To Data Bus
8
Figure 38
RXCn
73
TXCn
D Setting MR2n[7:6] = 01 places the channel in the Auto-
matic Echo Mode, which automatically re-transmits
the received data. Figure 39 presents a diagram de-
picting Automatic Echo Mode Operation. The follow-
ing conditions apply while in this mode.
(Parallel data from the CPU)
Transmit Shift Register
From Data Bus.
8
XR88C681
TXDn
Transmit Holding
Register
Outgoing Serial
Data