PC0801ARS-F datasheet(32/65 Pages) POWERTIP

32 / 65 page

ST7066U

V2.0

2001/03/01

9/42

Function Description

#" System Interface

This chip has all two kinds of interface type with MPU : 4-bit bus and 8-bit bus. 4-bit bus or 8-bit bus is selected

by DL bit in the instruction register.

During read or write operation, two 8-bit registers are used. One is data register (DR), the other is instruction

The data register(DR) is used as temporary data storage place for being written into or read from

DDRAM/CGRAM, target RAM is selected by RAM address setting instruction. Each internal operation, reading

from or writing into RAM, is done automatically. So to speak, after MPU reads DR data, the data in the next

DDRAM/CGRAM address is transferred into DR automatically. Also after MPU writes data to DR, the data in DR

is transferred into DDRAM/CGRAM automatically.

The Instruction register(IR) is used only to store instruction code transferred from MPU. MPU cannot use it to

read instruction data.

To select register, use RS input pin in 4-bit/8-bit bus mode.

Table 1. Various kinds of operations according to RS and R/W bits.

#" Busy Flag (BF)

When BF = "High”, it indicates that the internal operation is being processed. So during this time the next

instruction cannot be accepted. BF can be read, when RS = Low and R/W = High (Read Instruction Operation),

through DB7 port. Before executing the next instruction, be sure that BF is not High.

#" Address Counter (AC)

Address Counter(AC) stores DDRAM/CGRAM address, transferred from IR.

After writing into (reading from) DDRAM/CGRAM, AC is automatically increased (decreased) by 1.

When RS = "Low" and R/W = "High", AC can be read through DB0 ~ DB6 ports.

RS R/W

Operation

Instruction Write operation (MPU writes Instruction code

into IR)

Read Busy Flag(DB7) and address counter (DB0 ~ DB6)

Data Write operation (MPU writes data into DR)

Data Read operation (MPU reads data from DR)

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