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I'm using a slot sensor (break beam) as part of my shaft encoding. the slot
sensor is reading the number of breaks when the 6 spokes (attached to the
shaft) spins. i'm using the Sencdr1.icb file to do drive the shaft encoder.
i notice that there isn't a great change in the velocity calculated by the the
shaft encoder & driver. what's the problem??
here's the code for the driver:
* handy board shaft encoders
* simple (non-quadrature) encoder
* with hysteresis on counting transitions
* samples at 250 Hz. rate
* operates off of system interrupt
* Fred Martin
* 22 Apr 1996
* 6811 registers
BASE EQU $1000
ADCTL EQU $1030 ; A/D Control/status Register
ADR1 EQU $1031 ; A/D Result Register 1
TOC4INT EQU $E2 ; Timer Output Compare 4
ANLGPORT EQU 1
* zero-page global variables
system_time_hi EQU $12
system_time_lo EQU $14
ORG MAIN_START
* low and high thresholds for counting pulses
variable_encoder1_low_threshold: FDB 50
variable_encoder1_high_threshold: FDB 200
* tick and velocity counts
variable_encoder1_counts: FDB 0
variable_encoder1_velocity: FDB 0
* internal variables
encoder_state: FCB 0
last_counts: FDB 0
* install module into 1 kHz IC system interrupt on TOC4
subroutine_initialize_module:
LDX #$BF00 ; pointer to interrupt base
* install ourselves onto system interrupt
* get current vector; poke such that when we finish, we go there
LDD TOC4INT,X ; SystemInt on TOC4
STD interrupt_code_exit+1
* install ourself as new vector
LDD #interrupt_code_start
STD TOC4INT,X
* reset encoder variables
LDD #0
STAA encoder_state
STD variable_encoder1_counts
STD variable_encoder1_velocity
STD last_counts
RTS
* encoder interrupt code:
* check for transition every 4th time called (250 Hz)
* calculate velocities at about 16 Hertz (exactly: 1000 / 64 Hz.)
interrupt_code_start:
LDAA system_time_lo+1 ; lowest byte
ANDA #%00000011
BNE interrupt_code_exit
LDX #BASE
* get analog reading
LDAA #ANLGPORT
STAA ADCTL,X
BRCLR ADCTL,X $80 *
LDAA ADR1,X
TST encoder_state
* if zero, look for rising edge
BNE test_falling
CMPA variable_encoder1_high_threshold+1
BLO encdr_done
* got it! increment
got_click:
LDY variable_encoder1_counts
INY
STY variable_encoder1_counts
LDAA encoder_state
EORA #$FF
STAA encoder_state
BRA encdr_done
test_falling:
CMPA variable_encoder1_low_threshold+1
BLO got_click
encdr_done:
* calc velocities every 64 calls
LDAA system_time_lo+1 ; lowest byte
ANDA #%001111111
BNE interrupt_code_exit
* velocities are ticks since last interrupt
LDD variable_encoder1_counts
SUBD last_counts
STD variable_encoder1_velocity
LDD variable_encoder1_counts
STD last_counts
interrupt_code_exit:
JMP $0000 /* this value poked in by init routine */
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