Serial Communication Interface (SCI) - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 466

DS14C232 1

DCD

6

DSR

2

14

11

RxD

PS1/TxD T1 IN T1 OUT

7

8 RTS

10

CTS 1 R2 IN

T2 IN

3

13

12

PS0/RxD TxD

R1 OUT R1 IN

7 8

CTS

9

RTS 1

T2 OUT

R2 OUT

4

DTR

Note: 1. Both CTS and RTS are

jumpered to an I/O pin in case
hardware handshake is needed.

9

RI

5

GND

DB9 connector

Figure 9.18 ■ Diagram of SCI and EIA-233DB9 connector wiring in SSE256 demo board

Example 9.3
▼ Write a subroutine to send a break to the communication port controlled by the
SCI0 interface. The duration of the break is approximately 24,000 E-clock cycles, or 1 ms
at 24 MHz.
Solution: A break character is represented by 10 or 11 consecutive 0s and can be sent out by
setting the bit 0 of the SCI0CR2 register. As long as the bit 0 of the SCI0CR2 register remains
set, the SCI will keep sending out the break character. The following assembly subroutine will
perform the desired operation:

#include “c:\miniide\hcs12.inc”

sendbrk bset SCI0CR2,SBK ; turn on send break

ldy #1

jsr delayby1ms

bclr SCI0CR2,SBK ; turn off send break

rts

#include “c:\miniide\delay.asm”