Difference between revisions of "NU32v2: Using the LS7183 Quadrature Clock Converter"
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'''THIS PAGE REFERS TO A PRE-RELEASE VERSION OF THE NU32 PIC32 DEVELOPMENT BOARD. FOR INFORMATION, SAMPLE CODE, AND VIDEOS RELATED TO THE PRODUCTION VERSION (2016 AND LATER), AND TO THE CORRESPONDING BOOK "EMBEDDED COMPUTING AND MECHATRONICS WITH THE PIC32 MICROCONTROLLER," VISIT [[NU32|THE NU32 PAGE]].''' |
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The LS7183 quadrature clock converter is a chip used to convert quadrature signals from encoders into up and down counts that can be sent to a microchip. |
The LS7183 quadrature clock converter is a chip used to convert quadrature signals from encoders into up and down counts that can be sent to a microchip. |
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== Details == |
== Details == |
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[[Image:LS7183.png|center]] |
[[Image:LS7183.png|center|thumb|400 px]] |
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The resistor bias is used to control the pulse width of the up and down counts. The mode (1X, 2X, 4X) is used to multiply the |
The resistor bias is used to control the pulse width of the up and down counts. The mode (1X, 2X, 4X) is used to multiply the quadrature clock rate by 1, 2 or 4. The mode is selected by connecting MODE to |
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* VSS (GND) -> 1X |
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* VDD (3.3V) -> 2X |
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* Float (don't connect to anything; in practice, though, you may have to connect it to a floating input of the PIC32 to get reliable behavior) -> 4X |
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The UP and DOWN count pins should be connected to external counters on the PIC32. |
The UP and DOWN count pins should be connected to external counters on the PIC32. |
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== Sample Code == |
== Sample Code == |
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The full code can be downloaded [[Media:NU32v2_Encoder.c | here]]. The code configures 2 external counters (see [[NU32v2: Counters and Timers#External Counter|Counters and Timers]]) that will increment with each pulse received from the LS7183. The example sends the encoder position via RS232 to your PC. |
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The main piece of code shown below reads the UP and DOWN counters. With a variable called bigcount, it adds the the recent UP counts, subtracts the down counts and adjusts for roll-over of the counters. The full code placed this code in the main while loop, but this code can be placed in an ISR if you want to read the encoder at a given rate. |
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<pre> |
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count0 = ReadTimer4(); // in your routine this must be done at least every 32000 |
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// encoder counts to avoid rollover ambiguity |
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count1 = ReadTimer5(); |
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bigcount += count0 - last0; // add on the recent up-counts, since the last time |
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if (count0 < last0){ |
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bigcount += 65536; // count0 only increments, so if it got lower |
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//it must have rolled over |
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} |
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last0 = count0; |
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bigcount -= count1 - last1; // we're not worrying about rollover of the 32 bit bigcount total |
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if (count1 < last1){ |
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bigcount -= 65536; |
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} |
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last1 = count1; |
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</pre> |
Latest revision as of 06:28, 16 January 2016
THIS PAGE REFERS TO A PRE-RELEASE VERSION OF THE NU32 PIC32 DEVELOPMENT BOARD. FOR INFORMATION, SAMPLE CODE, AND VIDEOS RELATED TO THE PRODUCTION VERSION (2016 AND LATER), AND TO THE CORRESPONDING BOOK "EMBEDDED COMPUTING AND MECHATRONICS WITH THE PIC32 MICROCONTROLLER," VISIT THE NU32 PAGE.
The LS7183 quadrature clock converter is a chip used to convert quadrature signals from encoders into up and down counts that can be sent to a microchip.
Overview
Rotary encoders create quadrature signals on two channels (A and B) corresponding to the speed and direction of a motor. Some encoders produce up to a million counts per revolution. For very fast quadrature signals there is no way that a software quadrature decoder can avoid overrun errors. Instead we may use the LS7183 chip to translate the A and B quadrature signals into brief pulses indicating up-count or down-count. The up and down counts can be configured as external input signals to increment counters on the PIC32. By reading the counters on the PIC, we can determine the angle of the motor.
Details
The resistor bias is used to control the pulse width of the up and down counts. The mode (1X, 2X, 4X) is used to multiply the quadrature clock rate by 1, 2 or 4. The mode is selected by connecting MODE to
- VSS (GND) -> 1X
- VDD (3.3V) -> 2X
- Float (don't connect to anything; in practice, though, you may have to connect it to a floating input of the PIC32 to get reliable behavior) -> 4X
The UP and DOWN count pins should be connected to external counters on the PIC32.
Sample Code
The full code can be downloaded here. The code configures 2 external counters (see Counters and Timers) that will increment with each pulse received from the LS7183. The example sends the encoder position via RS232 to your PC.
The main piece of code shown below reads the UP and DOWN counters. With a variable called bigcount, it adds the the recent UP counts, subtracts the down counts and adjusts for roll-over of the counters. The full code placed this code in the main while loop, but this code can be placed in an ISR if you want to read the encoder at a given rate.
count0 = ReadTimer4(); // in your routine this must be done at least every 32000 // encoder counts to avoid rollover ambiguity count1 = ReadTimer5(); bigcount += count0 - last0; // add on the recent up-counts, since the last time if (count0 < last0){ bigcount += 65536; // count0 only increments, so if it got lower //it must have rolled over } last0 = count0; bigcount -= count1 - last1; // we're not worrying about rollover of the 32 bit bigcount total if (count1 < last1){ bigcount -= 65536; } last1 = count1;