24 | I RCA COSMAC VIP Instruction Manual |
A single photocell input could be provided via the buffered EF4 line. You can attach the photocell directly between the L and Z pads. Experimentally adjust the
this input byte in RAM.
also latch
Using the Expansion
Interface
The
You can latch up the required high order address bits with the trailing edge of TPA when adding external memory. You must provide a Positive level on pad 19 to disable internal RAM when external RAM is addressed. The operating system will always use the highest page of internal
If you wish to substitute an external ROM or
The expansion interface pads provide access to all CDP1802 signals so that you can add any desired external circuits.
Only 5 out of the possible 14 CDP1802 input/output instructions are used internally, so that you can externally decode the N0, N1, and N2 lines and use them with MRD to obtain the use of the remaining 9 input/output instruction codes. You can
Some Expansion Ideas
The August and September 1976 issues of Popular Electronics contain descriptions of a COSMAC ELF microcomputer using the CDP1802. These articles illustrate some input/output attachment techniques.
The following lists some things that with some exercise of your ingenuity could be added to your system at relatively low cost:
1.Manually operated photoelectric
2.Scanning circuit for multiple input lines from
sensing devices using CD4515 IC.
3.Full alphanumeric keyboard.
4.
5.
6.Calculator chip.
7.Individual photocells or switches.
8.Output relays to control solenoids, bells, whistles, sirens, lights, or motors.
9.
10.
11.
12.
13.Alpha wave monitor input to control pictures on TV or output devices.
14.Temperature- or
15.Computer terminal.
16.A second hex keyboard for