Shevek <[EMAIL PROTECTED]> wrote:
> On my computer, I have connected the printer port, the joystick
> ports and the cassette port to some easy-accessable plugs. I'm
> planning on doing the cartridge slots, too. The joystick and the
> printer port are easy to access, and so is the tape motor. My
> question is: How do I send data to the tape output and what kind of
> signal will be on it when I do so? A connected question: What kind
> of signal should I give the input-line in order to get a 0 or a 1,
> when reading it? I've disassembled the bios and it looks like it I
> have to put &H0A or &H0B on i/o-port &HAB to make it high or low.
> But it didn't give any voltage, when measured. Does anyone know how
> to do this? Thanks, shevek
The cassette connector is for connecting to a cassette recorder, and
therefore doesn't input/output digital signals, but audio signals.
For the cassette out (to the MICrophone input of a cassette
recorder), it's an audio signal with a voltage level in the order of
10's of millivolts, and only passes through signals in a limited
frequency range (some 10's up to a couple of KHz.). So no use for
controlling anything. It's coupled to register C, bit 5 of the PPI
(Programmable Peripheral Interface, a 8255 or compatible IC).
The cassette input takes an audio signal. Same limitation here:
frequency limited, and no exactly defined or fixed input levels. This
signal is input through Port A, bit 7 of the PSG (Programmable Sound
Generator).
The cassette motor connections are usually simply hooked up to a
relais (that's giving the well known clicks when giving MOTOR ON or
OFF), and it's controlled through register C, bit 4 of the PPI ('next
to' the cassette write signal), with "0" meaning "motor on".
The PSG is located starting at I/O-address A0h (-A2h), so to read the
casette input signal:
out (&hA0), 14 ;set PSG register 14 (=port A)
after this, bit 7 of I/O-port &hA2 contains the cassette input
signal.
For the PPI (on I/O-ports A8-ABh):
out (&hAA), inp (&hAA) and &b11101111 or:
out (&hAB), &b0xxx1000
("x" = don't care)
Sets cassette motor on,
out (&hAA), inp (&hAA) or &b00010000 or:
out (&hAB), &b0xxx1001
sets cassette motor off.
out (&hAA), inp (&hAA) or &b00100000 or:
out (&hAB), &b0xxx1011
sets cassette output ("MIC") to "1"
out (&hAA), inp (&hAA) and &b11011111 or:
out (&hAB), &b0xxx1010
sets cassette output to "0"
The 1st instructions shown above, address PPI register C on its 'own'
I/O-address, the second instructions do the same, but in a different
way, by using a single bit set/reset function of register C of the
PPI (also used in the BIOS routines).
Ofcourse, you'd have to do some assembly programming to get a decent
audio frequency tone out of the cassette port.
If you're thinking of using it to control anything, like LED's,
relais, other hardware, I would use the printer port or the joystick
port instead.
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx (MSX Tech Doc page)
http://www.twente.nl/~cce/index.htm (Computerclub Enschede)
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