prindle@NADC.ARPA (Frank Prindle) (07/31/89)
Here is the C-64 MIDI interface schematic I promised. I've proofread it as
much as possible; there is always the possibility of a typo remaining, but
I think not.
-------------CUT HERE FOR PRINTING - NEXT 66 LINES SHOULD BE ON 1 PAGE---------
____ COMMODORE 64 MIDI INTERFACE (5 CHIP)
|xtal| Compatible with Siel/JMS(Jellinghaus)
*----------|-||-|----------* standard. Complete on this page.
| 2Mhz|____| |
| | Pages that follow discuss addressing of
*--\/\/\--* *--\/\/\--* 6850 chip, MIDI-THRU addition, mods for
| 2.2K | | 2.2K | Sequential or Passport compatibility.
| |\ | | |\ | |\
| | \ | || | | \ | | \
*--| >o--*--||--*--| >o--*--| >o--------*----* +5V
| / 51pf|| | / | / | | v
|/ |/ |/ Rx| Tx| |
CLK| CLK| Vcc|
+5V>-----*----\/\/\---* .--------------.
| 270 | | 3 4 12 | ___ ___
MIDI-IN DIN Jack .-------. | | 7|-IRQ--->IRQ (pin 4)
5<>--------------*--|2 6 | | | |
| | 4|--------*--Rx-|2 10|-CS1--->A2 (pin W)
2<>--N/C diode V | PC- | DATA| |
--- | 900 | | 11|-RS---->A0 (pin Y)
220 | | 5|------* | | _
4<>-------\/\/\--*--|1 | | | 13|-R/W--->A1 (pin X)
'-------' V | 6850 |
GND | ACIA 14|-E----->02 (pin E)
/| /| | |
MIDI-OUT DIN Jack / | / | | 15|-D7---->D7 (pin 14)
5<>----\/\/\------o< |----o< |--------Tx-|6 16|-D6---->D6 (pin 15)
220 \ | \ | DATA| 17|-D5---->D5 (pin 16)
2<>---* \| \| | 18|-D4---->D4 (pin 17)
| | 19|-D3---->D3 (pin 18)
V | 20|-D2---->D2 (pin 19)
GND 220 |\ | 21|-D1---->D1 (pin 20)
4<>-------\/\/\---<+5V | \ | 22|-D0---->D0 (pin 21)
*---| >o---CS0-|8 |
| | / | 1 5 9 23 24 |
|\ | |/ '--------------'
| \ | | | | | | |
A6 <----| >o-----------|2 | *-*-*-*---*-------*
(Pin S) | / | | _ _ _ ___ |
|/ |\ | | V R C D CTS V
| \ | | s T S C GND
A5 <---------| >o------|1 | s S 2 D
(Pin T) | / | |
|\ |/ | *-----*
| \ |--_ |
A4 <----| >o-----------|3 \ | NOTES:
(Pin U) | / | 74 \ |
|/ |\ |LS30 |o--* 1. All inverter/buffers are (1/6)74LS366
| \ | / with pins 1, 8, and 15 grounded; pin
A3 <---------| >o------|12 / 16 supplied with +5V. 2 chips needed.
(Pin V) | / |---
|\ |/ | 2. A .01 uf bypass capacitor from Vcc to
___ | \ | GND at each chip is not a bad idea.
IO1<----| >o-----------|11
(Pin 7) | / | 3. I'm not entirely sure about the 51pf
|/ +5V | capacitor in the clock circuit; it
^ *---|4 may need a different value to oscil-
| | | late depending on the crystal used.
+5V<---------*------*---|5
(Pin 2) | | 4. The PC900 optoisolator available from
*---|6 MIX Bookshelf, 6400 Hollis St. #12,
GND | | Emeryville, CA 94608; price is $3.00
^ *---|14(Vcc) including postage.
| |
GND<---------*----------|7 (GND) 5. All (Pin #) numbers refer to the C64
(Pin 1) | cartridge port connector CN6.
To add a MIDI-THRU output jack, it will be necessary to add another 74LS366
chip, since two more inverters are required. Simply connect the output from
pin 4 of the PC900 optoisolator to the following circuit in addition to pin
2 of the 6850:
/| /|
MIDI-THRU DIN Jack / | / |
5<>----\/\/\------o< |----o< |--------- from pin 4 of PC900
220 \ | \ |
2<>---* \| \|
|
V
GND 220
4<>-------\/\/\---<+5V
A 6N138 optoisolator is the only acceptable substitute for the PC900. Its pin-
out is different:
PC900 Pin Corresponding 6N138 Pin
1 2
2 3
4 6
5 5
6 8
As shown in the main schematic, the 6850 is addressible in the C-64 I/O
address space $DE04-$DE07 and is clocked at 2MHz. This is the Siel/JMS
standard. The following table shows the addressible 6850 registers and control
register settings for the 3 common standards:
Siel/JMS Passport Sequential
Control Register Address DE04 DE08 DE00
Transmit Data Register Address DE05 DE09 DE01
Status Register Address DE06 DE08 DE02
Receive Data Register Address DE07 DE09 DE03
Master Chip Reset Command 03 03 03
Enable Xmit/Rcv 16 15 15
Enable Xmit/Rcv + Rcv Interrupt 96 95 95
Enable Xmit/Rcv + Xmit Interrupt 36 35 35
Enable Xmit/Rcv + Both Interrupts B6 B5 B5
Please consult the Motorola MC6850 Data Sheets for details on programming the
6850. As you can see, all three interface standards are very similar. The
only two differences are:
_
1. The way the address lines and the R/W line from the C-64 are decoded.
2. The 6850 clock frequency - in the Siel/JMS standard it is 2Mhz, in the
others it is 500KHz. Therefore, for the Siel/JMS standard, the 6850 must
be commanded to divide the clock by 64 to achieve the MIDI bit-rate of
31250; but the Passport and Sequential standards only require it to divide
by 16; thus the difference in the low 2 command bits.
Any software package may be compatible with one or more of the common stand-
ards; if it is not inherently compatible, either s/w or h/w must be modified.
Therefore, I propose the following (unconfirmed) modifications to the circuit
for compatibility with Passport or Sequential standards.
Passport:
1. Connect pin 10 of the 6850 (CS1) to A3 (Pin V) instead of A2 (Pin W).
2. Connect A2 (Pin W) to the inverter input which had come from A3 (Pin V).
_ _
3. Connect pin 13 of the 6850 (R/W) to R/W (Pin 5) instead of A1 (Pin X).
___
4. Connect pin 9 of the 6850 (CS2) to A1 (Pin X) instead of GND.
5. Disconnect the 6850 clock inputs at pins 3 and 4 and insert a divide-by-4
circuit between the last clock inverter output and pins 3/4. An example
of such a circuit is:
\ .---------.
\ | 14|----< +5V
>o-----|11 |
/ | 74LS293 |
/ *---|12 4|--------*----*
| | 7 | | |
V '---------' Rx| Tx|
GND | CLK| CLK|
V .-----------
GND | 3 4
Sequential:
1. Connect pin 10 of the 6850 (CS1) to pin 8 of the same chip (CS2) instead of
to A2 (Pin W). This parallels CS1 and CS2.
___
2. Connect pin 9 of the 6850 (CS2) to A2 (Pin W) instead of GND.
3. Add the same divide by 4 clock circuit as shown above for Passport.
One final note: any software package which uses the "smart" features of a
specific interface (i.e. it's on-board clock(s), tape/drum sync, foot switch
interfaces, etc.) will probably not work unmodified with this simple MIDI
(UART only) interface. However, a vast majority of public-domain S/W will
work fine as long as the standard supported is one of the 3 above and the
hardware or the software is modified to match. Also beware that the Siel/JMS
standard (also DATEL) is the LEAST likely to be supported by software in
the U.S. (Passport is perhaps the MOST supported, with Sequential running a
close second).
Sincerely,
Frank Prindle
Prindle@NADC.arpascott@max.acs.washington.edu (08/02/89)
In article <POSTNEWS24024@NADC.ARPA>, prindle@NADC.ARPA (Frank Prindle) writes: > Here is the C-64 MIDI interface schematic I promised. I've proofread it as > much as possible; there is always the possibility of a typo remaining, but > I think not. > hardware or the software is modified to match. Also beware that the Siel/JMS > standard (also DATEL) is the LEAST likely to be supported by software in > the U.S. (Passport is perhaps the MOST supported, with Sequential running a > close second). " " " " " " " " " " > Sincerely, > Frank Prindle > Prindle@NADC.arpa Thanks for the Schematics......It must have taken you a lot of time; the MIDI schematic that you drew was very impressive. I appreciated very much. Scott K. Stephen