Z89340 datasheet(24/30 Pages) ZILOG

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Z89340

Digital Wavetable Engine

1-24

P R E L I M I N A R Y

DS96DSP0201

OSCILLATOR PARAMETER BLOCKS (Continued)

Effects Send Control

address C

Effects Attenuation(s)

bits 0-5

These six bits control the amount of signal that will be sent

to the selected Effects Channel (bits 6-7). Since the signal

will be sent to two effects output channels if the Dual Effect

Sends bit in the Control Byte is set, the Effects attenuation

splits into two 3-bit attenuation values, with bits 0-2 as the

attenuation for the channel selected by the Effects Chan-

nel, and bits 3-5 as the attenuation for the subsequent

channel.

Effects Channel

bits 6-7

These two bits are used to select one of four effects output

channels. These output channels can be used internally by

the Z89340, and they can also be sent to a DAC or CO-

DEC. If the Dual Effect Sends bit in the Control Byte is set,

the signal will be sent to two effects channels, the one se-

lected here and the subsequent channel.

Envelope rate

address D

When ATFP selects Amplitude, Filter, or Pan:

Envelope Rate

bits 0-7

With Amplitude, the eight bits of Envelope Rate are an un-

signed exponential representation of the slope between

the amplitudes at the two envelope segment ends. This is

the rate that defines how long it will take to reach the end

amplitude, Amplitude Next. An interrupt is generated when

the segment end is reached, at which time the host CPU

will set up the next amplitude segment, supplying a new

Amplitude Next value and Envelope rate. A similar proce-

dure is followed when ATFP selects Filter or Pan.

When ATFP selects Tremolo:

Tremolo Rate

bits 0-3

The four bits of Rate are an unsigned exponential number

that give rates ranging from 0.1 to 10 Hz.

Tremolo Depth

bits 4-7

These four bits specify depths of 1.5 to 24 decibels.

Amp/Filt/Pan Next

address E

When ATFP selects Amplitude:

Amplitude Next

bits 0-7

Amplitude is expressed in an unsigned logarithmic unit

called a hexadecibel or “hexabel” for short. The upper four

bits of the hexabel are a base-two exponent and the lower

four bits form the mantissa. There are 256 hexabel steps

in 96 decibels, so 2.667 hexabels = 1 decibel. At the initial-

ization of a note, set Amplitude Now and Amplitude Next

with the endpoints of an amplitude envelope segment.

Also set the Envelope Rate. For subsequent amplitude en-

velope segments, only set Amplitude Next and Envelope

Rate, because Amplitude Now always equals Amplitude

Next at the end of an envelope segment.

When ATFP selects Filter:

Filter Tuning Next

bits 0-7

Filter Tuning Next works in a way similar to Amplitude

Next.At the initialization of a filter envelop segment, set Fil-

ter Tuning value and Filter Tuning Next with the endpoints

of the filter envelope segment. Also set the Envelope Rate.

When ATFP selects Pan:

Pan Angle Next

bits 0-5

Pan Next works in a way similar to Amplitude Next or Filter

Tuning Next, except that there are only six bits of pan po-

sition. At the initialization of a pan segment, set Polar Pan

Angle and Pan Angle Next with the endpoints of the pan

envelope segment. Also set the Envelope Rate.

Pan Direction

bit 6

A 1 indicates counterclockwise rotation, and a 0 indicates

clockwise rotation.

Pan Continuous Loop

bit 7

If this bit is a 0, an interrupt is generated to let the host CPU

know that the panning has completed. If this bit is set, pan

continues around this circle indefinitely. No interrupt is

generated when Pan Angle Next is reached.

Amplitude Now

address F bits 0-7

(Refer to the previous discussion on Amplitude Next.) If

ATFP amplitude envelopes are not being used, this will be

the amplitude of the oscillator—a steady or sustained am-

plitude segment. Amplitude Now can be changed whenev-

er desired; however, changing Amplitude Now more than

1 hexabel will usually cause a noticeable click. Even a 1

hexabel change will sometimes cause a click. To eliminate

clicks or zipper noise, use the amplitude envelope system.

Polar Pan Control

address 10

Polar Pan Angle

bits 0-5

There are four main output channels. The spatial location

among them is specified with a modified polar coordi-

nate—a value of 16 is

π/2 radians, 32 is π radians, 48 is

π/2 radians, and so on.

Polar Pan Radius

bits 6-7

The radius select is a two-bit number with 2 at the edge of

the circle and 0 near the center of the circle. A radius of 3

is reserved for stereo panning when only two output chan-

nels are needed. When the radius is 3, the following spe-

cial values of Pan Polar Angle are defined:

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