Q
I would like to use the multiprocessor feature of the serial interface of the
ADuC812, in which bit 9 causes an serial interrupt if set. Unfortunately I
can't get this feature working, so I wonder if there is a software error or if
this feature is missing in the ADuC812. Here is my code:
$MOD812 ; use ADuC812 predefined symbols
CSEG
ORG 0000h
LJMP START
ORG 0023h
LJMP SERIAL_INT
ORG 0030h
START:
MOV SCON,#11110000B ; Mode 3, 9 bit, receive enable
MOV TMOD,#20H ; timer 0 no function
; timer 1 mode 2
MOV PCON,#00H ; set SMOD
MOV TH1,#100H-3 ; reload 3 = 11.0592MHz/12/16/2/9600 bd
SETB TR1 ; start timer
SETB ES ; enable serial interrupt
CLR PS ; serial interrupt low priority
SETB EA ; general interrupt enable
LOOP:
JMP LOOP ; repeat indefinately
SERIAL_INT:
PUSH PSW
PUSH ACC
MOV A,SBUF ; get character
CPL P3.4 ; toggle LED
CLR RI ; clear receive flag
POP ACC
POP PSW
RETI
END
This program should run directly on the evaluation board, it toggles the LED
each time it gets a serial interrupt. Now I send data from my PC with and
without bit9 set, but both cause the interrupt. I ensure the PC program is
correct by looking at the signals with a digital scope.
P.S.: Can I run the ADuC812 with an 11,0592MHZ quartz at 115200 baud?
A
This is a known bug on the ADuC812 and covered in item 3 of the current Errata
sheet (REV E). The full errata sheet is available on our website:
www.analog.com/microconverter
3. UART FUNCTION - MULTIPROCESSOR COMMUNICATIONS MODE :
Background: UART Modes 2 and 3 (programmed via SCON) have a special provision
for multiprocessor communications. In these modes, nine data bits are
received and the ninth bit goes into RB8. In this mode the port can be
programmed so that when the stop bit is received, the serial port interrupt
is activated only if RB8(SCON) = 1. This feature is enabled by setting the
SM2 bit in SCON.
Issue: With SM2 set, the serial port interrupt is set each time a stop bit is
received, regardless of the state of the RB8 bit.
Work-Around : Implement a software polling scheme in the Serial Port ISR so
that the
state of the RB8 bit is checked on entering the ISR. If RB8 is ‘0’ then a
‘RETI’ is executed to exit the ISR immediately, and only if RB8 is set will
the ISR function be executed.
Related Issues : None.