Quadrature decoders are used to determine the angle of rotation of
an axis. The rotation direction, rotation speed and position of the
rotor is important for many applications. Most industry available decoders
chips have 16 or 24 bit counters, what usually are not big enough
for some applications. Position count of this Quadrature Decoder can
be easily extended from 32 till 64 bits. The idea is employed on site:
http://www.mcselec.com/an_115.htm.
We added controller software with implemented simple digital filter
and fast parallel communication interface.
Schematics
Communication protocol
Data are synchronized using PD0 and PD1 pins in handshaking mode.
By default PD0 and PD1 are set to 1.
Command : "Reset Counter" (00).
1. External controller sets pins PD5, PD6 to 0. (Command: reset counter
)
2. External controller sets Enable pin to 0. (Synchronization. Low
level is active)
3. AT90S2313 detects Enable signal low level , resets internal Counter
to zero, and sets Data_Ready pin to 0 (command is done).
4. External controller detects Data_Ready signal low level and sets
Enable pin to 1.
5. AT90S2313 detects high Enable signal and sets Data_Ready pin to
1.
Command: "Read first (lowest) byte" (10).
1. External controller sets pins PD5 to 0, PD6 to 1. (Command: read
lowest byte)
2. External controller sets Enable pin to 0. (Synchronization. Low
level is active)
3. AT90S2313 detects Enable signal low level, sends Lowest Counter
data byte to PB port and sets Data_Ready pin to 0 (command is done).
4. External controller detects Data_Ready signal low level, reads
data byte from PB output and sets Enable pin to 1.
5. AT90S2313 detects high Enable signal and sets Data_Ready signal
to 1.
Command: "Read second or next byte" (01).
1. External controller sets pins PD5 to 1, PD6 to 0. (Command: read
next byte)
2. External controller sets Enable pin to 0. (Synchronization. Low
level is active)
3. AT90S2313 detects Enable signal low level, sends next Counter
data byte to PB port and sets Data_Ready pin to 0 (command is done).
4. External controller detects Data_Ready signal low level, reads
data byte from PB output and sets Enable pin to 1.
5. AT90S2313 detects high Enable signal and sets Data_Ready signal
to 1.
Command: "Reserved" (11). The command
is employed to make any response.
1. External controller sets pins PD5 to 1, PD6 to 1. (Reserved command:
do nothing)
2. External controller sets Enable pin to 0. (Synchronization. Low
level is active)
3. AT90S2313 detects Enable signal low level and sets Data_Ready
pin to 0 (command is done).
4. External controller detects Data_Ready signal low level and sets
Enable pin to 1.
5. AT90S2313 detects high Enable signal and sets Data_Ready signal
to 1.
Instruction, how to read signed long
integer (4 bytes = 32bits: Range -2147483648 to 2147483647) from AT90S2313
chip.The sequence of commands is: "Read lowest
byte", "Read second or next byte", "Read second or next byte", "Read
second or next byte". Actually, external controller can read
only 1 byte (lowest), or only 2 bytes, or only 3 bytes, if more significant
bits are no more important.
Software
Note: The Freeware is tested on prototype board and supplied as it is. The author disclaims all warranties of any kind.
Every AVR flash controller needs embedded software. Download open code C project for CodeVisionAVR Standard. The compiler available on HP InfoTech. Noncommercial size limited version works as well. Download compiled Hex file, ready to load into AT90S2313 chip
AT90S2313 chip programmer PG302 is available from Iguana Labs.
