The COSMAC VIP was designed primarily as a self-contained graphic system for home use. Enough RAM and input/output features are provided for years of computer fun without adding anything to your system. If, however, you do want to expand your system, a variety of features have been included to make expansion as easy and inexpensive as possible. You can easily increase RAM to 4096 bytes by adding U20-U23to your PC card. Use the same type or a compatible type of RAM as used for U16-U19. You may, however, have to add a higher-current power supply when expanding RAM.
Using the Byte
Input/Output
First, you may wish to add some external com- puter-controlled devices such as relays, input sensing switches, or even a low-cost printer. The printer will require an 8-bit parallel input or output port and some "hand-shaking" signals. One parallel input port and one parallel output port are available on the PC card as shown in Fig. E-5 in Appendix E. These ports are provided by U24, U25, U26, and U27 along with the associated resistors and two IN914 diodes. The 22 input/output port connection pads (A-Z)along the back right edge of the PC card are connected to a standard 44-pin card socket on the COSMAC VIP board. You can plug your external circuits or devices into this socket. Table II gives the input/output port terminal connections.
The 8 buffered output signals (M,N,P,R,S,T,U,V) will each drive up to 2 TTL loads. A 63 machine language instruction will latch a memory byte into U24 for output. The 8 latched output lines can be used to drive individual relay driver circuits, power amplifiers, lights, battery motor drivers, etc. The
buffered Q output line (W) can be used as an output strobe for transferring the latched output byte to an external device such as a printer. The EF3 (X) and EF4
(L)input fines can be used to indicate the status of an external device. Don't forget that EF3 is shared with the hex keyboard.
Table 11 - Input/Output Port Terminal Connections (See Fig. E-5, Appendix E)
