Z89340 Datasheet, PDF (22/30 Pages) Zilog, Inc. – Digital Wavetable Engine

Z89340
Digital Wavetable Engine
OSCILLATOR PARAMETER BLOCKS (Continued)
Frequency Low
address 1
Envelope-type ATFP
bits 0 and 1
Four types of envelope segments are supported, but only
one at a time. Amplitude/Tremolo/Filter/Pan Envelope-
type control bits.
00-Amplitude
01-Tremolo
10-Filter
11-Pan.
Frequency Low
bits 2-7
These are the lowest six bits of the 22-bit linear frequency
Frequency Mid
address 2
bits 0-7
These are the middle eight bits of the 22-bit linear frequen-
cy.
Frequency Hi
address 3
Frequency Hi
bits 0-7
(Sample Loop Oscillator only)
These are the highest eight bits of the 22-bit linear fre-
quency. Frequency is represented as a linear two's-com-
plement value. A negative frequency plays the sound
backwards.
Frequency Hi
bits 0-3
(Wavetable Mode Oscillator only)
These are the highest four bits of the 18-bit linear frequen-
cy. Frequency is represented as an unsigned linear value.
With the Wavetable Mode Oscillator, the upper four bits
are an extended opcode and must be 0100; negative fre-
quencies are not possible with the remaining 18 bits of lin-
ear frequency.
Extended Opcode
bits 4-7
(Wavetable Mode Oscillator only)
With the Wavetable Mode Oscillator, the upper four bits of
Frequency Hi are one of the extended opcodes and must
be 0100.
Phase
address 4
Phase
bits 0-7
The eight bits of Phase, along with the 16 bits of Wave
Pointer Mid and Lo, are that part of the wave address that
is modified by the oscillator through the life of the note as
it steps from sample to sample based on frequency. The
upper bits of the wave ROM address are set at initialization
and remain fixed (Wave Pointer Hi). Wave Pointer Lo
points to a sample in ROM or RAM. Phase gives the dis-
tance between the sample and the subsequent sample.
The oscillator does a piecewise linear interpolation be-
tween the two samples. To further reduce conversion er-
ror, eight bits of smoothing are added below Phase in the
internal processing. Phase is generally given a value of 0
at the start of a note.
Wave Pointer Hi
address 5
ROM16-ROM23
bits 0-7
The eight bits of Wave Pointer Hi control wave ROM or
RAM address lines 16-23, which are the highest address
bits. This value remains fixed throughout the life of a note.
The lower bits of Wave Pointer are changed by the Z89340
during the life of a sound until they equal Wave Endpoint.
ROM23/DMA
bit 7
If DMA bus-mastering mode is enabled, this bit enables
DMA for the oscillator. The address then becomes an ISA
Bus host CPU RAM address. DMA has system conse-
quences and should be used with caution. In particular,
fewer oscillators can be active at the same time. Tape
Loops should not be used because of limitations of data
transmission across the ISA bus.
Wave Pointer Lo
address 6
ROM0-ROM7
bits 0-7
The eight bits of Wave Pointer Lo are part of the wave ad-
dress that is modified by the oscillator through the life of
the note as it steps from sample to sample based on fre-
quency corresponding to ROM or RAM address bits 0-7.
The upper bits of the wave ROM address are set at initial-
ization and remain fixed (Wave Pointer Hi). Wave Pointer
Lo points to a sample in ROM or RAM. (Refer to Phase
and Wave Pointer Mid.) Wave Pointer Lo contains the low-
est bits of the start address when a note is begun.
Wave Pointer Lo and Wave Pointer Mid are changed by
the Z89340 during the life of a sound until they are equal
Wave Endpoint.
Wave Pointer Mid
address 7
ROM8-ROM15
bits 0-7
The eight bits of Wave Pointer Mid point to a block of 256
samples. This 256 sample block can be considered a
wavetable for use in wavetable synthesis. For sample-se-
quence playback, Wave Pointer Mid forms the upper eight
bits of the 16-bit sample pointer; Wave Pointer Lo holds
the lower eight bits. This allows sample sequences of up
to 64K samples. Wave Pointer Mid contains eight bits of
the start address when a note is begun. Wave Pointer Lo
and Wave Pointer Mid are changed by the Z89340 during
the life of a sound until they equal Wave Endpoint.
1-22
PRELIMINARY
DS96DSP0201