Notes: Omron

Notes: Omron

Revision: 4.6

Download this page along with the Memory Usage and Wiring Diagrams as a Microsoft Word file "Notes.doc" for best printing. This file is included on the disks that come with the MSP and with all driver downloads.

What is an MSP Driver? An MSP driver is a small ladder logic program that is added to the user program. All code is standard ladder logic. In Omron PLCs it requires one line of logic in the main program and one to three subroutines. The line of logic in the main program sets up a time interrupt. Subroutine "0" is called by the time interrupt. Subroutine "0" may be the complete driver or in some versions it may call one or two other subroutines.

The user can import the driver into their program threw the "Network/Block Manager" or they can start with our driver and build their program from it.

Drivers. The following is a list of drivers in the MSP Driver Library for the Omron CPM1 PLC. These drivers were prepared with Omron's Syswin 2.1 programming software. The single channel input and single channel output drivers are available on the Driver Installation disks. All other drivers are available on our web site. They contain rung comments, address descriptions, and address symbols that are viewable in the programming package and on printouts.

DRIVER	DESCRIPTION
Msp_I	1 Channel Input
Msp_I_M	2 Channel Input Multiplexed
Msp_I_H	1 Channel Input High-Speed Counter
Msp_O	1 Channel Output
Msp_O_M	2 Channel Output Multiplexed
Msp_IO	1 Channel Input, 1 Channel Output
Msp_IO_M	2 Channel Input Multiplexed, 2 Channel Output Multiplexed

Different Models. All drivers for the CPM1 should work with very little revision on other Omron models. Omron's programming language and memory layout is very similar in all models.

a) The CPM1A is virtually identical to the CPM1 and the drivers should work without revision.

b) The CPM1A is a subset of the CQM1 and the drivers should work without revision. This model is available with solid state outputs therefore output speed can be increased without worry about relay life. The output modules are available in both sink and source versions. See the sections on inputs and output regarding these modules.

Timing Parameters. These drivers are set up for the Delta protocol. Following are some of the key timing parameters:

Input
Protocol	Delta
Scan Time	10 msec (See Note 8)
Full Word Bits	16 Bits
Delta Bits	4 Bits
Delta Refresh Count	16 Scan Refresh
ID Pulse Width	1.2 Scans
Data Pulse Width	3 Scans
Output
Protocol	Delta
Scan Time	50 msec (See Note 8)
Full Word Bits	16 Bits
Delta Bits	4 Bits
Delta Refresh Count	16 Scan Refresh
ID Pulse Width	3 Scans
Data Pulse Width	3 Scans

Scan Time. The key to getting the driver to function properly is to get the driver code executed and PLC I/O for the MSP updated at constant time intervals.

The CPM1 PLCs executes the driver code in a time interrupt subroutine. The time interrupt is set up with the Scheduled Time Interrupt Mode (STIM) instruction. This is a very powerful and complex instruction that has multiple uses. We found this instruction worked slightly different than the manual described. It may also work slightly different in your PLC.

The answer to many of the questions on the STIM instruction can be found in the Omron manual "Sysmac CPM1 Programmable Controller, Programming Manual." There are two sections that require special attention. The first is section 1.3.4 "Interval Timer Interrupts." The second is section 5.15.5 "Interval Timer - STIM(69)". The second section is basically repeat the first but is more concise. If you do not have this manual you it is strongly recommended that you get it.

One other nasty trick to remember is that STIM used this way uses Timer 0. Timer 0 cannot be used in the program for any other purpose.

The MSP driver uses the STIM instruction set for mode 3, Scheduled Interrupt Mode. The mode is set in "Data 1" as always a constant and does not require the "#". "Data 2" is the interrupt time. When set as a constant the units are msec. Normally it is set to 10 msec. "Data 3" is the subroutine number set to "0" (zero). Note that when "Data 2" and "Data 3" are entered as constants they must be proceeded by the "#". If "Data 2" is entered as an address it actually uses two consecutive addresses and the units can be different. See the Omron manuals for more details. We recommend that it be left as a constant.

The STIM can be a difficult instruction and may require careful study and trial and error experiments. It is a very powerful and versatile instruction. We put in a life counter to tell when the time interrupt is running and to measure its time. Every time the interrupt subroutine is run we added one to the life sign register. You should see this register continually ramp up and then rap around and ramp up again. This rung may be deleted after you get the driver running.

Inputs are updated in the beginning the STIM subroutine using the I/O Refresh (IORF) instruction. Outputs are set at the end also by using the I/O Refresh (IORF) instruction. See the Omron help files or manuals on how the I/O Refresh instructions work. If changing the I/O point used for the MSP these instruction may also have to be modified.

Quality Control File. Included with the files for each driver is a file of the same name with the ".sp" extension. This file contains the model and serial numbers of all hardware and software used for testing. This file also contains the setup parameters used for testing.

Scan Time Exceptions. When possible the scan time is set at 10 msec. This is the default setting of the MSP. On some older models it may have to be slowed down. Those models with relay outputs must be slowed down when using MSP analog outputs. The mechanical relays are slow when compared to solid state and we us a scan time of 50 msec. Note that the Msp_IO_M driver effectively has 4 channels. For any of the multiplexed drivers that are expanded to 4 or more channels on any model the scan time should be watched closely and may have to be increased.

Programming Methods. One of the key programming methods is the use of memory locations that are accessed both as registers and bits. We used the HR memory for this purpose. Other memory types are acceptable with the exception of DM memory. In several cases we use a shift register as a counters. A seed is planted in bit zero of the shift register word. To increment the counter by one the shift resistor is shifted one bit. This allows the current value of counter to be checked by testing a single bit in ladder, which is much more efficient than a whole register compare. Omron's ASL instruction makes this very efficient. These programs have been extremely optimized for both minimum scan time and memory usage.

Programming Results. Programming for these processors yields fairly clean and understandable code. The ASL instruction make shift register counters very efficient. Omron's register compare is very clumsy when considering inline compares in many other brands. In some stances it adds a considerable number of parallel branches.

Much of Omron’s math is centered around BCD although it has both Binary and BCD math. Our protocol and many of the programming methods used are binary. Our input and output data are in binary. Care must be taken when using analog values in the program to avoid improper mixing of data types. You must also remember that binary multiplies put the result in two memory locations.

The ladder logic has been refined and optimized to a very high degree. In someways this may make the driver programs harder to read but it is felt that efficient use of memory and execution time are the most important factors.

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