Specifications

Serial Communications (V40)
FUNCTIONAL DESCRIPTION
The SCU is similar to the 8251 Serial Control Unit for asynchronous
operation. The SCU does not support synchronous communication
protocols. Figure 10-1 shows a functional block diagram of the SCU.
A description of each functional block follows.
SST
(Status Register)
SCM
(Command
Register)
SRB
(Receive
Data Buffer)
STB
(Transmit
Data Buffer)
SMD
(Mode Register)
SIMK
(Interrupt
Mask Register)
RESET CLOCK
IORD
IOWR
A2
A1
EN
RTCLK
RxD
TxD
SINT (to ICU)
Internal Data Bus (Higher or Lower 8 Bits)
SCU Status and Control Bus
Read/Write
Control
Receiver
Transmitter
Interrupt
Generation Logic
(8)
(8)
Figure 10–1. SCU Block Diagram.
10-3