ST7066

V1.2

2000/6/13

21

Interfacing to the MPU

The ST7066 can send data in either two 4-bit operations or one 8-bit operation, thus allowing interfacing with 4- or

8-bit MPU.

!" For 4-bit interface data, only four bus lines (DB4 to DB7) are used for transfer. Bus lines DB0 to DB3 are

disabled. The data transfer between the ST7066 and the MPU is completed after the 4-bit data has been

transferred twice. As for the order of data transfer, the four high order bits (for 8-bit operation, DB4 to DB7) are

transferred before the four low order bits (for 8-bit operation, DB0 to DB3). The busy flag must be checked (one

instruction) after the 4-bit data has been transferred twice. Two more 4-bit operations then transfer the busy flag

and address counter data.

!" For 8-bit interface data, all eight bus lines (DB0 to DB7) are used.

Supply Voltage for LCD Drive

There are different voltages that supply to ST7066’s pin (V1 - V5) to obtain LCD drive waveform. The relations of the

bias, duty factor and supply voltages are shown as below:

Duty Factor

1/8, 1/11

1/16

Bias

Supply Voltage

1/4

1/5

V1

V2

V3

V4

V5

R

R

R

R

R

VR

R

R

R

R

VR

V1

V1

Vcc

V2

V3

V4

V5

Vcc

V2

V3

V4

V5

-5V

+5V

-5V

1/4 bias

(1/8, 1/11 duty

cycle)

1/5 bias

(1/16 duty

cycle)