was young, The ZX Spectrum was the cheapest of the 8 bits, and
frequently looked down upon by CPC and C64 owners... Despite its more
limited graphics, they do yield some interesting advantages... compared
to the CPCs 4 color mode 1... the ZX Spectrum has similar resolution,
and twice the onscreen colors - what's more, it uses half the screen
memory which means Spectrum games are often significantly smoother than
their CPC equivalents...
These days, clever developers are able to work around the spectrums color limitations, and produce impressive looking games with fast gameplay on this classic 8 bit.
|0||Tone Pitch L - Channel A||LLLLLLLL||Lower value = Higher pitch|
|1||Tone Pitch H - Channel A||----HHHH||Lower value = Higher pitch|
|2||Tone Pitch L - Channel B||LLLLLLLL||Lower value = Higher pitch|
|3||Tone Pitch H - Channel B||----HHHH||Lower value = Higher pitch|
|4||Tone Pitch L - Channel C||LLLLLLLL||Lower value = Higher pitch|
|5||Tone Pitch H - Channel C||----HHHH||Lower value = Higher pitch|
|6||Noise Generator||---NNNNN||Higer = Faster noise|
|7||Mixer||--NNNTTT||N=Noise T=Tone (Channel --CBACBA 1=mute 0=normal)|
|8||Amplitude - Channel A||---EVVVV||E=Envelope (1=Enabled) VVVV=Volume|
|9||Amplitude - Channel B||---EVVVV||E=Envelope (1=Enabled) VVVV=Volume|
|10||Amplitude - Channel C||---EVVVV||E=Envelope (1=Enabled) VVVV=Volume|
|11||Envelope L (Volume over time)||LLLLLLLL||Lower=Faster Envelope|
|12||Envelope H (Volume over time)||HHHHHHHH||Lower=Faster Envelope|
|13||Envelope Selection||----EEEE||Envelope number (See PDF)|
|The "Beeper" sound chip is incredibly crude... it is
controlled by bit 5 of the port &FE... by turning it on and off
can make simple sounds...
See the example to the right... by changing the pause (caused by BC) we can change the pitch of the sound... 3000 will be a relatively low pitch... 500 will be higher...
Some clever programs even manage to "Fake" multiple sound channels!
The big disadvantage to all this is that the CPU will be busy during the whole time, so the Beeper chip isn't very helpful, and we'll want to use the AY sound chip on the 128k systems... but on the 48k machines, it's all we've got!
| xor a
xor %00010000 ;---S-BBB S=Sound B=Border
ld bc,3000 ;Lower number=higher pitch
|&7FFD||&5B5C||- - IRSMMM||MMM= ram bank at C000 (0-7) S=Screen page bit R=Rom Low bit I=I/O Disabling|
|&1FFD||&5B67||- - - SDR - P||P = paging mode (0=norma 1=+3) R=Rom high bit D = Disk Motor S=Printer strobe|
|&4000||Screen 1 (5)*|
|&C000||Screen 2 (7)|
|Ram 0||Ram 0|
|Ram 1||Ram 1|
|Ram 3||Ram 3|
|Ram 4||Ram 4|
|Ram 6||Ram 6|
|&1FFD Bits 2,1|
|&C000||Bank 3||Bank 7||Bank 3||Bank 3|
|&8000||Bank 2||Bank 6||Bank 6||Bank 6|
|&4000||Bank 1||Bank 5 (S)||Bank 5 (S)||Bank 7 (S)|
|&0000||Bank 0||Bank 4||Bank 4||Bank 4|