J041 SCPUB

Using the SCPUB

Because the SCPUB can be configured in so many different ways, it is difficult to make many general recommendations about using it, mainly because the software will determine exactly how it is used. There are two obvious situations where it can be employed, and a summary of them may suggest other possibilities.

As a target system

Software can be developed on another computer, then transferred in EPROM or downloaded into RAM. A useful approach is to have a machine code monitor in one EPROM socket, so that the code can be debugged on the SCPUB.

As a development system

Alternatively, software can be developed on the SCPUB itself. The addition of a floppy disk drive and controller enables the user to run the wide range of programs available under the CP/M operating system.

One such program is the A880 Arcom BASIC compiler. This allows the programmer the ease of writing in a high-Ievel language, with the speed of Z80 machine code. AB80 contains driver routines to save BASIC source text or object code programs in EPROM using the Arcom STEbus EPROM programmer.

Finally the finished object code application program is blown into EPROM, plugged into one EPROM socket of a target SCPUB, and a run-time package EPROM plugged in the other.

AB80 is also available in EPROM to provide a low initial system cost option. There are some general points to note when using the board for the first time.

  1. If you are using it with any other STE boards on the bus, a terminated bus should be used. This is partly to reduce reflections, although these are not usually serious on short buses, and partly because some lines are open-collector and require pull-ups.
  2. If you are not using it on a bus, power can be connected via the 5 pin connector PL2. Check that the connections are correct with an ohmmeter between your power supply ground and pin 7 IC7 (and 504) on the board.
  3. The normal terminal connection is to channel A of the DART. Output from the SCPUB is pin 1 of PL3, input to it is on pin 2, and ground is on pins 5, 11 and 12. Terminal connections and set-up information for specific software such as the SCPUB monitor and BASIC are provided in the appropriate software manual.
  4. A reset switch may be connected via 2 pins of connector PL4.
  5. It is possible to use more than one processor board on the bus for multiprocessing applications. However, the SCPUB does not have a bus arbiter. This means that another board with a bus arbiter (for example, a SYSCON) must also be in the system, and the SCPUB must be jumpered to accept bus acknowledge signals. Two SCPUBs may be used with an external arbiter, provided they are jumpered to different request/acknowledge levels. With more than one processor in the system, ensure that SYSCLK comes from only one board. Processors can communicate with each other by common memory or I/O locations. A convenient way of doing this is via the I/O mapped memory in the real-time clock of a SCRAM board.
  6. Boards are tested with jumpers in the standard configuration shown in Section 4. If you have altered the jumpers and the board does not work, restore the jumpers to the original setting and try the board with some standard software (for example the EAMONB Monitor) to check whether the SCPUB is operating correctly.