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.
- 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.
- 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.
- 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.
- A reset switch may be connected via 2 pins of connector
PL4.
- 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.
- 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.