w65c51n Western Design Center, Inc., w65c51n Datasheet - Page 26

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

+5
LLB
SEL
STB
1B
2B
3B
4B
74157
1Y
2Y
3Y
4Y
1A
2A
3A
4A
PROCESSOR
MICRO-
RTSB DTRB TxD
PROGRAM
ROM
Figure 19 Loop-Back Circuit Schematic
Figure 18 Simplified System Diagram
SYSTEM
RAM
SEL
STB
1B
2B
3B
4B
W65C51S
Notes: 1. HIGH ON LLB SELECTS LOCAL LOOP-BACK MODE
74157
2. HIGH ON 74157 SELECT INPUT GATES “B” INPUTS TO
“Y” OUTPUTS; LOW GATES “A” TO “Y”.
1Y
2Y
3Y
4Y
1A
2A
3A
4A
CONTROL
RxD DCDB CTSB DSRB
I/O
I/O
TO DATA LINK
W65C51S
MODEM
ACIA
DCDB
CTSB
DSRB
DTRB
RTSB
RxD
TxD
MODEM
26