HARDWAREPERIPHERIQUES ★ CPC-Digiblaster v2.0 ★

Sound - Digiblaster v2Hardware Peripheriques
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CPC-Digiblaster : The sound of the printer port.

The original Text was written by A.Stroiczek and the DMV-Verlag (CPC International 8/9'91), the hardwarelayout of the Digiblaster v2.0 was performed by Joshua/Exodus and converted by Tim Riemann (TCS-Software@gmx.de).

Please mail me if there are any mistakes (especially my bad english ;-) ! If we're looking at the 16bit computers like Amiga, Atari ST, Mac and PC (with a soundcard) the CPC users can be jealous. We can help with an easy circuit plan.

The CPC only can do rectangle frequencies. Amiga and other computers are working with digital instruments which they give out with internal D/A converters. If you look exactly the CPC has the possibility to give out digital instruments. For this you need the volume register. This register can handle 16 different volumes. So it may be possible to play samples with 4bit. But the soundchip dissapoints again.

To play a linear volumeincrease the power at the sound port is logarithmical. This means that you have to change the values so that they are linear. So you only have 3bit. The Amiga has a advantage with his 8bit samples. If you say: "Okay, half bits are enough" you are wrong. With 3 bits you can use 8 different values, with 8 bits 256. That means you cannot play low sounds.

Okay, if you don't look at the very difficult programming the CPC is not as good as his colleagues. But the meagre printer port allows you to change that.
To play 8bit samples you need a 8bit interface and a circuit which changes the values in a power value. The printer port has 8bit and a 5V power supply (Bit 7 = STROBE).

The printer port makes it possible

To build a D/A unit you normally need a special IC which costs about 15 to 20 DM and it needs an own power supply. The circuit here costs about 3 to 12 DM and does not need an own power supply. But because of this the output power is not exactly linear.You can connect the output of the circuit directly to an amplifier.

All good things are three

Of course, the D/A unit needs a small demo program. Because sampled instruments are very long I only have printed the file 'DATA1.BAS'. Start it and hear a little sound. Strangly it sounds much better when the upper ROM is selected.

The programming

The program writes directly to the hardware of the CPC. You can use the port with the adress &EFxx. Because the CPC has only a 7bit printer port (we need 8bit for the Digiblaster) we use the STROBE signal, which is inverted by the hardware, so you have to invert your sound value. Now we want to output the value &C5:

LD a,&C5     ;A=&C5
LD B,&EF     ;load the port adress
XOR &80      ;invert the 7th bit
OUT (C),A    ;out to the printer port

The accu is the register A.
The parallel port has the following connects:

PIN 1              STROBE
PIN 2              D0
PIN 3              D1
PIN 4              D2
PIN 5              D3
PIN 6              D4
PIN 7              D5
PIN 8              D6
PIN 9              GND
PIN 11             BUSY
PIN 14             GND
PIN 16 to PIN 28   GND
PIN 33             GND

The pins that are not named are not connected.

Easy converting

How often you print out the values it is called the sampling rate. This value shall be three times higher than the highest frequency. It is possible to play some instruments at the same time. You have to add the values and divide them. I think that 4 channel sound is possible with the CPC.
A.Stroiczek

Well, here is the circuit plan:

Parts you need:

D1-D8 1N4148
R1 1k
R2 110k
R3 18k
R4 51k
R5 13k
R6,R7,R8 16k
R9 4k7
R10 3k3
R11,R12,R13 2k
R14 470

Sorry, I hadn't enough time to draw the circuit plan properly (maybe that's something you could do ;-)!

Converted 1996/1998 by Tim Riemann (TCS-Software@gmx.de)

★ YEARS: 1996 , 1998
★ AUTHOR: TIM RIEMANN

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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent  du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.