Commodore has recently introduced a new line of low-cost computer systems for home users. Using over a quarter of a million transistors inside 70 ICs, the PET is probably one of the most complicated simple devices ever built by man. Yet, even a child can operate it. Like PAIA, Commodore is making new technology available at a minimum cost.

PET includes a keyboard, cassette recorder, and TV monitor all built into one 44 lb. case. Like its forefathers, the Jolt and KIM, PET uses a 6502 microprocessor. It has a 14K firmware system (including 8K BASIC, 4K operating system, 1K machine language monitor, and 1K diagnostic routine) and is available with either 4K or 8K of user memory. For outside expansion, there are 4 plug-in connectors on the back and side of PET, which include an IEEE-48 intelligent interface, a memory expansion connector, a second cassette interface, and an 8 bit parallel user port. It is the user port in which we will be most interested for interfacing PET to PAIA.

HARDWARE INTERFACING

Simple! The PAIA 8780 Digital to Analog Converter module connects easily to PET using a 12 and a 24 pin edge connector and a couple of feet of 10 conductor cable. The connectors are available from most mail order houses or can be fabricated by cutting a Radio Shack 44 pin connector into the proper lengths.

CONTROL SOFTWARE

PET can talk in two "languages", BASIC (the easier of the two to use) and machine (or Assembly) language.

BASIC is a high level language designed to be learned quickly by beginning programmers and is simple enough that even children can learn to write short programs. There are quite a few books and magazine articles available on learning BASIC so I'm not going into the language itself here; only where it applies to PET's musical abilities.

The output port on PET is software accessible by the following BASIC commands:

POKE 59459,255 (sets the in/out port to OUTPUT)
POKE 59457,N (sets the port DATA lines to "1". N = a number (note) between 0 and 255)

If N = 0 nothing comes out of the 8780 D/A (rest).
If N = 1 to 63, a note is set on the output of the 8780.
If N = 64, triggers flag #1.
If N = 128, triggers flag #2.

To play a note using the 8780 to trigger a function generator and control a VCO you first set the I/O to output using POKE 59459,255 (this need only be done once at the beginning of the program). Then set the note with POKE 59457,N (so the VCO can settle) then trigger the flag with POKE 59457,N=64 (sets flag #1 and keeps VCO at same note. Hopefully, you have connected flag #1 to the ADSR trigger!). Then reset the trigger by POKE 59457,N (VCO still holding). Then reset the note by POKE 59457,0 and start all over again. NOTE: The above does not take into account TIME. PET BASIC is a very fast keyboardist, you have to slow things down in order to hear them properly! Use the program in example #1 to play a song (?) with PET.

MACHINE LANGUAGE

BASIC can play the 8780 fast but is not nearly fast enough for a QuASH (Quad Addressable Sample & Hold), so we switch to a lower level, but much faster language called Assembly language. PET has the capability of running both in BASIC and machine language in the same program by using the USR and SYS commands.

PAIA's Poly 1.0 and MUS1 should be usable with some modification, in PET since they were written in 6500 series Assembly Language.

I am now in the process of converting them for PET and will cover the conversion in a future article. For now, BASIC is doing an exceptional job in the performing arts. Definitely, the PAIA/PET combination is the way to go.

Listed below are descriptions of three music programs available for the PET.

PET MUSE 1. 0 — designed for multitracked sound effects.
PET COMPOSER — PET composes and plays infinite variety of "songs" (true computer music).
PET-MUSE — turns PET into a quality sequencer with over 500 note capability. Includes one classical song.

These and over 40 other PET programs are available on cassette for $2.50 for the first program and $1.50 for each additional program ($4.00 minimum order) postpaid from;

PET LIBRARY c/o Russell Grokett (Contact Details)

Send a SASE for a list of all programs available.