6172 CAN Micro Controller Module

The 6172 is a digital I/O device, capable of interfacing various A/D - D/A converters (and of course various other digital devices) with the CAN bus, using a application layer protocol (like CANopen or DeviceNet).

From the application layer viewpoint, the 6172 is a node with 1024 digital inputs and 1024 digital outputs, all of which can be accessed via 128 parameters, attributes, objects, etc (depends on how the application layer calls them).

In CANopen, all these in-/outputs can be accessed using SDO (and PDO) :

• read from object 6000h (digital inputs), subindex 1..128, one byte per subindex, subindex 97..112 are reserved
• read from object 6100h (digital inputs), subindex 1..48, two bytes per subindex
• read from object 6120h (digital inputs), subindex 1..24, four bytes per subindex
• write to object 6200h (digital outputs), subindex 1..128, one byte per subindex , subindex 97..112 are reserved
• write to object 6300h (digital outputs), subindex 1..48, two bytes per subindex
• write to object 6320h (digital outputs), subindex 1..24, four bytes per subindex

The 6172 I/O (as seen from the CAN bus) is a 128 byte memory with special meaning to some locations (for more information look in the sequencer description):

 

Location	Symbolic name	Description	connector/pin
0 - 95	-	general purpose RAM	-
96 - 106	-	reserved for future use	-
107	RSCFG	Sets RS232 configuration	3/3 3/5 3/6 3/8
108	RSOUT	Shift-out memory location via RS232 interface
109	RSIN	Shift-in memory location from RS232 interface
110	RSRBL	Get amount of received characters in RS232 buffer
111	RSTBF	Get amount of free characters in RS232 buffer
112 113	PWMFL, PWMFH	Sets PWM output frequency	3/2
114 115	PWMDL, PWMDH	Sets PWM output duty cycle
116	MISC	Miscellaneous commands	-
117	I2OUT	Writing this location shifts the data out the I2C interface	3/11 3/12
118	I2IN	Reading this location returns a byte shifted in from the I2C interface
119	SPISPD	Configures the SPI shifter BAUD rate	2/17 2/18 2/20
120	SPIPAT	Configures the SPI shifter clock polarity/phase and LSB/MSB first
121	SPIOUT	Writing this location shifts the data out the SPI shifter
122	SPIIN	Reading this location returns a byte shifted in from the SPI shifter
123	PORTA	Write parallel output port A, read the last written data	1/2 - 1/12
124	PORTB	Write parallel output port B, read the last written data	1/14 - 1/18
125	PORTC	Read parallel input port C	2/2 - 2/12
126	AIN1	Read 8 bits analogue input 1	3/14
127	AIN2	Read 8 bits analogue input 2	3/15

It is possible to access all 128 locations directly from the CAN bus (via parameter/attribute/object read/write messages).

Example:

A 24 bit shift register (like 3 pieces of CD4094) is connected to the (SPI) shifter, the 3 latch inputs are connected to PortA, bit 0 (out1). Assuming the shifter is already configured (with values in 'Config', 'Shift_Speed' and 'Shift_Pattern'), it takes 5 CAN messages to get 3 bytes of data to the outputs of these CD4094's:

1. Write 1th byte to 'SPIOUT'.
2. Write 2nd byte to 'SPIOUT'.
3. Write 3rd byte to 'SPIOUT'.
4. Set bit 0 of PORTA
5. Reset bit 0 of PORTA

It should be clear that this method consumes a lot of CAN bus bandwidth, time and effort. In a CANopen system using a busspeed of 125 kBAUD, this sequence will take at least 8.6 milliseconds.

To increase speed and decrease CAN bus load, the 6172 contains an internal sequencer which can perform some very basic tasks to move the data from internal RAM to the CD4094's. The task performed by the above 5 CAN messages can be executed by this sequencer in about 70 uS. The CAN bus load is decreased to just one message, which will take about 1.8 milliseconds (using CANopen SDO at 125 kBAUD) or 0.75 milliseconds (using a CANopen PDO).

To configure the sequencer to perform this simple task, a number of steps have to be taken:

1. Create sequencer program.
   In this case we will use sequence 3 and assume it starts at sequence program memory address 1140h, sequence is assembled in emulated mode.
   The sequencer program will look like this (the data should already be in memory location 0 .. 2):
   

   Address	Code	Data	Symbolic name	Action
   1140h	50h	0	SHOM	Shift out memory location 0
   1142h	50h	1	SHOM	Shift out memory location 1
   1144h	50h	2	SHOM	Shift out memory location 2
   1146h	11h	0	SETA	Output port A, set bit 0
   1148h	12h	0	RESA	Output port A, reset bit 0
   114Ah	7Fh	0	ENDSQ	end of sequence

2. Configure serial output port (SPI) and reset portA bit 0 in sequence 0 (after power on or reset)
   

   Address	Code	Data	Symbolic name	Action
   114Ch	12h	0	RESA	Output port A, reset bit 0
   114Eh	52h	1	SHSPD	Shift speed is 1.1 uS / bit
   1150h	53h	2	SHPAT	Shift pattern is standard
   1152h	73h	0	SRDY	Activate READY output
   1154h	7Bh	3	ENASQ	Enable sequence 3
   1156h	7Fh	0	ENDSQ	end of sequence

3. Configure sequence table:
   

   Address	Data	Description
   1000h .. 101Fh	xxx	ID data, free to use by user
   1020h	20	Sequencer version number
   1021h	0	No native code
   1022h	0	Reserved
   1023h .. 103Fh	0	No sequence starts on interval
   1040h	114Ch	Start address sequence 0 (initialization)
   1042h ..1045h	0	No sequence 1 or 2
   1046h	1140h	Start address sequence 3 (the actual function)
   1044h .. 107Fh	0	No other sequences
   1080h .. 1081h	0	No sequence starts on write of locations 0, 1
   1082h	3	Sequence 3 starts on write of locations 2
   1083h .. 10DFh	0	No sequence starts on write of locations 3 .. 95
   10E0h .. 113Fh	0	No sequence starts on read of locations 0 .. 95

   
   NOTE: generating the sequencer code and tables is made easy using the free available CDSystems Sequence Assembler
4. Write the contents of the sequence table (in this case just addresses 1000h .. 1157h) to the 6172 (CANopen object 2100h, subindex 0, 1th byte is that of adress 1000h).
5. Reset the node
6. Write data (first the data for RAM location 0, then 1, then 2) to the sequencer RAM, the sequence will start as soon as location 2 is written, causing the data to be transferred into the CD4094's.