Z89340 datasheet(22/30 Pages) ZILOG

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Z89340

Digital Wavetable Engine

1-22

P R E L I M I N A R Y

DS96DSP0201

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.

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