Amdrum

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Box and Manual for the Amdrum

A drumkit by the British company Cheetah.

The drumkit was able to play 8bit sound samples.

Quality of the playback was nice, considering the time and price.

The samples were read from the suplied tapes.

There were serveral tapes with different themes!.

Along with the Amdrum came a sequencing program.

It was possible to copy the samples to disc, but the sequencing program had to be patched!

Amdrum was probably Cheetahs version of the SpecDrum (As revealed on the PCB "AMSTRAD SPECDRUM")

No CPC emulator supports the Amdrum. To hear 'Amdrum' in action the Spectrum emulator Spectaculator emulates the SpecDrum.

No other software than Cheetahs own sequencer is know to use the Amdrum.

Technical Specifications

Uses I/O Port FFxxh (Write only), ie. only /IORQ, /WR, A15-A8 are decoded. A7..A0 are not decoded, and /RD isn't used, too.
Port usage: Write 8bit unsigned sample data to Port FFxxh. The D/A converter is mono and has only one channel (mixing multiple channels is to be done by software).
The Amdrum software uses port FFxxh. The playback routine also scans the keyboard. The lower 8-bits of the I/O port come from the last value of the C register used to scan the keyboard.

The five chips on the single-sided PCB are:

74LS30N	Single 8-input NAND	Port decoding, /ADDR_MATCH=LOW when A8..A15 all HIGH
74LS32N	Quad 2-input OR	Port decoding, /DAC_WRITE when /ADDR_MATCH, /IORQ, /WR all LOW
SN74LS04N	Hex Inverters	purpose unknown? (used in the analog part, not for Port decoding)
TL064CDP	Quad Amplifier	no info how the 4 amplifier stages are used?
Ferranti ZN428E-8	8bit DAC	mono one-channel 8bit D/A converter (unsigned samples)

ZN428 Datasheet - 8bit D/A Converter
TL064 Datasheet - Quad Amplifier

Partial dissassembly of player

exx     
ld      a,(bc)
add     a,(hl)
ex      de,hl
add     a,(hl)
inc     hl
ex      de,hl
inc     bc
add     a,80h
inc     hl
exx     
out     (c),a
ld      b,0f6h
in      a,(c)
ld      c,a
xor     05h
out     (c),a
ld      a,0f4h
in      a,(66h)
ld      (404eh),a
out     (c),c

ld      b,0ffh
nop     
nop     
nop     
exx     
ld      a,(bc)
add     a,(hl)
ex      de,hl
add     a,(hl)
inc     hl
ex      de,hl
inc     bc
add     a,80h
inc     hl
exx     
out     (c),a