AN1833 Freescale Semiconductor / Motorola, AN1833 Datasheet - Page 41

• Manufacturer Part Number: AN1833
• Description: A Low-Power Wireless Remote Control Transmitter and Receiver
• Manufacturer: Freescale Semiconductor / Motorola

************************************************************************************
* incoming/get_char -
* called by get_data
* input cond.
*
*
* get_char - receive one byte of data from RXD pin; called by main
*
* input cond.
* output cond.
*
*
* stack used
* variables used
*
* ROM used
************************************************************************************
incoming:
get_char
get_start_bit brclr
AN1833
MOTOROLA
STA
lda
sta
sta
sta
ldx
sta
incx
sta
incx
sta
incx
sta
incx
sta
rts
lda
sta
clrx
brset
lda
bsr
bsr
lsra
bne
tsta
tsta
lda
bsr
- expecting a preamble character of where four bits are logic 1
- followed by a series of 55 55 55
half carry = 1 (frame error occurred) or 0 (no frame error);
carry = 1 (noise and/or frame error occurred) or 0 (no noise)
count: temporary storage (1 byte)
buffer,x
buffer,x
TSCR
#$0
flag
char
length
#$0
buffer,x
buffer,x
buffer,x
- RXD pin defined as an input pin
- RXD pin defined as an input pin
- char contains received data; X,ACC undefined;
- 2 bytes
- char: storage for received data (1 byte)
- 63 bytes
#8
count
rxd,serial_port,*
rxd,serial_port,*
#BAUD_SEL-3
delay_13a
get_bit
get_start_bit
#2*(BAUD_SEL-2)
delay_13a
Freescale Semiconductor, Inc.
Routine from AN1240 written by Scott George
For More Information On This Product,
Go to: www.freescale.com
; C= RTI = enable, clear RTI Flag
; clear buffers
; clear 55 flag
; cleaar receiver memory location
; clear index counter
; clear receive buffer
; location 0
; location 1
; location 2
; location 3
;
;[2] receiving 8 data bits
;[4] store value into RAM
;[3] used to store noise data
;[5] wait until rxd=1
;[5] wait for start bit
;[2] prepare for 1/2 bit delay
;[13a+12] execute delay routine
;[39] sample start bit
;[3] noise bit -> carry;
;
;[3] if false start, start over
;[3] for timing purposes only
;[3] for timing purposes only
;[2] prepare for 1 bit delay
;[13a+12] execute delay routine
acc=filtered start bit
fx
fx
Application Note
Code Listing
41
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