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Tuesday, March 3, 2015

A little History and inner workings of FASTFINGERS

YES FastFingers is finished, but only as a standalone package or with the Mattel Intellivision Keyboard. They are both the same package, but there is a software SWITCH to turn on scanning the Mattel keyboard. Originally I never planned on a keyboard in the first year and 1/2 of development, but the Mattel keyboard was so inexpensive that I went ahead and started development.....but I should have looked at availability. It was being liquidated and I took my wife and my newborn daughter on a long roadtrip across Michigan to buy up all of the last ones from the Meijer department store chains. I was only able to get approx 15 units, and 10 of them were sold at the World of Commodore 1985. As to development time, it took another year to develop and tweak the Mattel Interface

So now I'm going to describe a bit of the workings of Mattel VS the PIC chip interface that I'm working on now, in a general way

The Mattel keyboard was being constantly scanned. It was an unusual system whereby I had to send out a signal to TURN ON a section of the keyboard (I think 8 keys at a time) and then READ back if one of those keys were PRESSED. Meanwhile , my effects and sequencer were interrupting every 1/240 of a second.

With the PIC chip, I'm using Serial on the MIDI side of the chip and parallel to send to the C64 UserPort. But this is tricky. If I don't clear the USART buffer on the PIC chip quick enough, it locks up. So now instead of updating 240 times a second I must POLL the UserPort 6000 or more times, per second, so that I can keep the buffer clear.So I have 2 more options left. I may add a hardware interrupt line or I may try (against my gut feeling) to insert the Userport read in the keyscan routine, (as it was setup for the Mattel)

Oh and the other level of complexity , is that I must also program the PIC chip, which has its' own unusual instruction set. That computer calls the accumulator the WORKING register. So movement is from and to W .....This is a cool 40 pin device only slightly larger than a SID chip....and here is an example of pic16f887 code

getmidi btfss PIR1,RCIF ; test for incoming data goto getmidi movf RCREG,W movwf RawMidi

movf RawMidi,W andlw 0xF0 ;filter sysex sublw 0xF0 bz start

movf RawMidi,W andlw 0xE0 ;filter pitch bend 1110 0000 sublw 0xE0 bz start

movf RawMidi,W andlw 0xD0 ;filter channel pressure aftertouch sublw 0xD0 bz start

movf RawMidi,W andlw 0xC0 ;filter program change sublw 0xC0 bz PrgmChng

movf RawMidi,W andlw 0xB0 ;filter control change sublw 0xB0 bz start

movf RawMidi,W andlw 0xA0 ;filter polyphonic aftertouch sublw 0xA0 bz start

YesMidi movf RawMidi,W andlw 0x90 sublw 0x90 bz GetNote movf RawMidi,W andlw 0x80 ;don't display status sublw 0x80 ;don't display status and disccard channel info bz NoteOff goto start

.and I have a 20mhz clock crystal on this board so this thing is 20X as fast as a C64