Epson S1C63558 4.12.5 Digital envelope

CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Sound Generator)

4.12.5 Digital envelope

A digital envelope for duty control can be added to the buzzer signal.

The envelope can be controlled by staged changing of the same duty envelope as detailed in Table 4.12.4.2 in the preceding item from level 1 (maximum) to level 8 (minimum).

The addition of an envelope to the buzzer signal can be done by writing "1" into ENON, but when "0" has been written it is not added.

When a buzzer signal output is begun (writing "1" into BZE) after setting ENON, the duty ratio shifts to level 1 (maximum) and changes in stages to level 8.

When attenuated down to level 8 (minimum), it is retained at that level. The duty ratio can be returned to maximum, by writing "1" into register ENRST during output of a envelope attached buzzer signal.

The envelope attenuation time (time for changing of the duty ratio) can be selected by the register ENRTM. The time for a 1 stage level change is 62.5 msec (16 Hz), when "0" has been written into ENRTM and 125 msec (8 Hz), when to "1" has been written. However, there is also a max. 4 msec error from envelope ON, up to the first change.

Figure 4.12.5.1 shows the timing chart of the digital envelope.

No change of duty level

BZFQ0–2

ENON

ENRST

ENRTM

BZE

BZ signal

Level 1

(Max.)

t11

duty ratio

2

t01

t01

3

4

t02

t12

5

t03

t13

6

t04

t14

7

t05

t15

8

(Min.)

t06

t16

t07

t17

t01

+0

+0

= 62.5 –4msec

t11 = 125 –4msec

t02–07= 62.5 msec

t12–17= 125 msec

Fig. 4.12.5.1 Timing chart for digital envelope

S1C63558 TECHNICAL MANUAL EPSON 103