w65c51n Western Design Center, Inc., w65c51n Datasheet - Page 18

• Manufacturer Part Number: w65c51n
• Description: Asynchronous Communications Interface Adapter Acia
• Manufacturer: Western Design Center, Inc.

Effect of CTSB on Echo Mode Operation
In Echo Mode, the Receiver operation is unaffected by CTSB, however, the Transmitter is affected when
CTSB goes high, ie., the TxD line immediately goes to a continuous “Mark” condition. In this case,
however, the Status Register indicates that the Receiver Data Register is full in response to an IRQB, so
the processor has no way of knowing that the Transmitter has ceased to echo. See Figure 12 for the
timing relationship of this mode.
CTSB
IRQB
RxD
TxD
P
Stop
Stop
Start
Start
B
0
B
0
CHAR # n
B
1
B
1
B
N
B
N
P
P
Stop
Figure 11 Effect of CTSB on Echo Mode
Stop
CTSB GOES TO
“FALSE” CONDITION
Start
Start
NORMAL
RECEIVER DATA
REGISTER FULL
INTERRUPTS
B
0
B
CHAR # n+1
0
B
1
B
1
B
2
B
N
P
Stop
CONTINUOUS “MARK” UNTIL CTSB GOES LOW
Start
NOT-CLEAR-TO-SEND
B
0
CHAR # n+2
B
1
B
N
P
Stop
Start
B
0
CHAR # n+3
B
1
B
N
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