This is one of my CNC motion control revisions and it is currently an work in progress.

CNC Controller Motion Board (Rev. C)

Table of Contents

• Introduction
• Design
• Schematics
• Printed Circuit Board
• Software
• Issues

Introduction

This is the Revision C version of my motion control board.

Design

I ultimately decided that the real problem with Revision B was I wanted to use a depower strategy for limit switched rather than an advisory strategy.

Communication between the two '628's is via a 3-wire phase bus that reports the low order 3 bits of the current axis position. This makes the communication `stateless'.

The board has no straps. None. Instead all configuration is performed through the parallel port interface in a special `configure' mode. The configuration information is stored in the EEPROM portion of the '628's.

The first PIC16F628 pin assignments are as follows:

Pin			Description
Number	Name	Kind
1	RA2/AN2	Analog In	Comparator2 Vin+
2	RA3/AN3/C10	Analog In	Comparator1 Vin+
3	RA4/TOCKI/CMP2	Digital In	Phase0
4	RA5/MCLR*/THV	Digital In	Phase1
5	VSS	Ground	Ground
6	RB0/INT	Digital Out	Motor0A
7	RB1/RX/DT	Digital In	Serial Input
8	RB2/TX/CK	Digital Out	Serial Output
9	RB3/CCP1	Digital Out	Motor0B
10	RB4/PGM	Digital Out	Motor0 Enable
11	RB5	Digital Out	Motor1A
12	RB6/T1OSO/TICK1	Digital Out	Motor1B
13	RB7/T1OSI	Digital Out	Motor1 Enable
14	VDD	Power	+5 Volts
15	RA6/OSC2/CLKOUT	Digital In	Phase2
16	RA7/OSC1/CLKIN	Digital In	Oscillator In
17	RA0/AN0	Analog In	Comparator1 Vin-
18	RA1/AN1	Analog In	Comparator2 Vin-

The second PIC16F628 pin assignments are listed in the following table:

Pin			Description
Number	Name	Kind
1	RA2/AN2	Digital Out	Phase2
2	RA3/AN3/C10	Digital In	Limit+
3	RA4/TOCKI/CMP2	Digital In	Home
4	RA5/MCLR*/THV	Digital In	Limit-
5	VSS	Ground	Ground
6	RB0/INT	Digital In	Step
7	RB1/RX/DT	Digital In	Serial In
8	RB2/TX/CK	Digital Out	Serial Out
9	RB3/CCP1	Digital In	Direction
10	RB4/PGM	Digital Out	DAC Clock
11	RB5	Digital I/O	DAC Data
12	RB6/T1OSO/TICK1	Digital In	Encoder0
13	RB7/T1OSI	Digital In	Encoder1
14	VDD	Power	+5 Volts
15	RA6/OSC2/CLKOUT	Digital In	Configure
16	RA7/OSC1/CLKIN	Digital In	Shared Oscillator In
17	RA0/AN0	Digital Out	Phase0
18	RA1/AN1	Digital Out	Phase1

Schematics

The schematics are broken into 1 connectors schematic and 4 relatively identical axis schematics.

The parts list is kept in a separate file.

The parallel port schematic is shown below:

The power supplyschematic is shown below:

The X Axis schematic is shown below:

The Y Axis schematic is shown below:

The Z Axis schematic is shown below:

The A Axis schematic is shown below:

The Patched Axis schematic is shown below:

Printed Circuit Board

The printed circuit board files are listed below:

• Artwork
• Back
• Front
• RS274-X `Gerber' Artwork
• RS274-X `Gerber' Solder Side
• RS274-X `Gerber' Component Side
• `Excellon' Drill File
• Tool File

Software

The software for the chopper microcontroller code is listed below:

chop.ucl

The µCL code for the chopper microcontroller.

chop.asm

The assembly code for the chopper microcontroller.

chop.lst

The assembly listing for the chopper microcontroller.

chop.hex

The Intel^® Hex file for the chopper microcontroller.

The code for the control microcontrollers is based on the code below. Due to some wiring mistakes on the Revision C board, I have to program each axis controller slightly differntly.

control.ucl

The µCL code for the control microcontroller.

control.asm

The assembly code for the control microcontroller.

control.lst

The assembly listing for the control microcontroller.

control.hex

The Intel^® Hex file for the control microcontroller.

xcontrol.ucl

The µCL code for the X control microcontroller.

xcontrol.asm

The assembly code for the X control microcontroller.

xcontrol.lst

The assembly listing for the X control microcontroller.

xcontrol.hex

The Intel^® Hex file for the X control microcontroller.

ycontrol.ucl

The µCL code for the Y control microcontroller.

ycontrol.asm

The assembly code for the Y control microcontroller.

ycontrol.lst

The assembly listing for the Y control microcontroller.

ycontrol.hex

The Intel^® Hex file for the Y control microcontroller.

zcontrol.ucl

The µCL code for the Z control microcontroller.

zcontrol.asm

The assembly code for the Z control microcontroller.

zcontrol.lst

The assembly listing for the Z control microcontroller.

zcontrol.hex

The Intel^® Hex file for the Z control microcontroller.

I never set up the forth A channel; hence, there is no software for the A axis microcontroller.

Issues

The following fabrication issues have come up:

• This is embarassing. The pins on the L298 are reversed. This means for this revision, the L298's need to go on the bottom.
• The MAX548A D/A converter needs to have the CS* pin raised and lowered to actually activate the commands. Oops.
• The output impedence of the MAX548 is an unbuffered 33K ohms. This means that the voltage divider needs to have its impedance kicked up by a factor of 10. Thus, use 390K and 100K resistors instead of 40K and 10K resistors.
• RA4 is an open drain output. It needs to have a resistor to pull it up.
• RA5 is a Schmitt trigger input only and has no output driver.
• Pin 3 of U23 should be tied high instead of low.
• The positive and negative terminals need to be marked on N12.
• The holes for the Schottky diodes D1-25 are too small and need to be made larger.
• The Schottky diodes are too close N1-4.
• The L298's (U13-16) are too close to N5-8.
• U24 is a little too close to N12 and N11.
• The hex nut will not fit between N2 and N3. Give it up.
• There is a thick track that shorts together Ground and VS on the Y and A channels. This is on the + end of D14 and D30.
• The R29-30 bias resistors should only be 100K instead of 1M.
• It may be necessary to relabel the pins for N5-8.
• The parallel port pins are labeled backwards from what they should be for a 25-pin parallel port connector; hence, the cable has to be twisted 180 degrees.
• The serial port pins are labeled backwards from what they should be for a 25-pin parallel port connector; hence, the cable has to be twisted 180 degrees.
• The parallel port is too close to N13.