AF Module Message Display CPU Replacement
Around 1984 Hill Graham Controls developed a variable speed AC drive based on the modified current source model. These drives were aimed at the high-power end of the market, reaching up to 8MW in output power.
Hill Graham Controls AF Module (c. 1990)
The first controller for this drive was call the AF Module (AF = Adjustable Frequency). This module was designed to be robust, reliable, repairable and maintainable and was arranged as a series of pages to allow access to all parts of the circuitry for fault finding and repair without having to use such things as card extenders or adapters which a rack system would need. It also had an internal ribbon bus to avoid using PC card connectors because these were viewed as a potential source of reliability problems.
The control circuitry was 100% analogue, except for the Message Display CPU board which used an 8-bit, 8MHz Z80 processor to drive a 2 line x 20 character LCD display to display internal and external trips and alarms. The program for the Z80 was held on a 64kbit UV eraseable EPROM. The program was written in PL/M (an obsolete Pascal-type programming language) which required a machine with a a CP/M operating system to compile and assemble the Z80 code.
If the Message Display CPU fails the AF Module is prevented from operating, even though the control circuitry is capable of operating independently.
CONTRELEC recently received some AF Modules for repair which were experience problems with the message display. After exhaustive hardware checks, which included re-programming the EPROM, a decision was made to replace the Z80 CPU, EPROM and RAM chips with a modern embedded processor. This would help future-proof the AF Module and allow program changes and updates to be made and debugged using a modern Integrated Development Environment (IDE).
The solution was realised using a Cypress PSOC 5 processor mounted on an adapter PCB which plugs directly into the vacant Z80 socket. The only hardware changes required are the removal of the aforementioned chips and the relocation of a decoupling capacitor on the Message Display PCB to the rear of the board, making it a simple plug-in solution.
The new code has been written using the C programming language.
The new processor is much easier to program and debug, and opens up opportunities for enhancement such as additional trips and alarms, multilingual display, etc. The new hardware also raises the possibility of adding a communications protocol to the AF Module for interfacing to information systems.
CONTRELEC can further help to prolong the service life of AF Modules by replacing the LCD Front Panel Meters as described here.