Department of Computer Scien

ce and Information Engineering

National Cheng Kung University

HANEL

8051

CONNECTION TO RS232MAX232

‰We need a line driver (voltage converter) to convert the R232’s signals to TTL voltage levels that will be acceptable to 8051’s TxD and RxD pins

MAX232 requires four capacitors MAX232 has two sets of line drivers

MAX232

8051

C3+

Vcc

C4+

16

2 6

1 3 4 5

+C1 +C2

T1in

T1outR1inT2outR2int

R1outT2inR2out

14 13 7 8

11 12 10 9

RS232 side

TTL side

15

MAX232

DB-9

1111 1012

142 133

5

P3.1TxD P3.0RxD