NJU6631A

s FUNCTIONAL DESCRIPTION

(1) Description for each blocks

(1-1) Register

The NJU6631A incorporates two 8-bit registers, an Instruction Register (IR) and a Data Register (DR).

The Register (IR) stores instruction codes such as “Clear Display” and “Return Home”, and address data for

Display Data RAM (DD RAM) and Character Generator RAM (CG RAM). The MPU can write the instruction

code and address data to the Register (IR), but it cannot read out from the Register (IR).

The Register (DR) is a temporary stored register, the data stored in the Register (DR) is written into the DD

RAM or CG RAM and read out from the DD RAM or CG RAM.

The data in the Register (DR) written by the MPU is transferred automatically to the DD RAM or CG RAM by

internal operation.

When the address data for the DD RAM or CG RAM is written into the Register (IR), the addressed data in

the DD RAM or CG RAM is transferred to the Register (DR). By the MPU read out the data in the Register

(DR), the data transmitting process is performed completely.

After reading the data in the Register (DR) by the MPU, the next address data in the DD RAM or CG RAM is

transferred automatically to the Register (DR) to provide for the next MPU reading.

These two registers are selected by the selection signal RS as shown below :

Table 1. shows register operation controlled by RS and R/W signals.

Table 1.

Register Operation

RS

R/W

Selected Register

Operation

0

0

Write

0

1

IR

∼DB

1

0

Write (DR to DD RAM or CG RAM)

1

1

DR

Read (DD RAM or CG RAM to DR)

(1-2) Busy Flag (BF)

When the internal circuits are in the operation mode, the busy flag is "1", and any instruction reading is

inhibited.

The next instruction should be written after busy flag (BF) goes to "0".

(1-3) Address Counter (AC)

The address Counter (AC) addressing the DD RAM and CG RAM.

When the address setting instruction is written into the Register (IR), the address information is transferred

from Register (IR) to counter (AC). The selection of either the DD RAM or CG RAM is also determined by this

instruction.

After writing (or reading) the display data to (or from) the DD RAM or CG RAM, the Counter (AC)

increments (or decrements) automatically.

∼DB

1.

(1-4) Display Data RAM (DD RAM)

The display data RAM (DD RAM) consists of 16 x 8 bits, stores up to 16-character display data represented

in 8-bit code.

The DD RAM address data set in the address Counter (AC) is represented in Hexadecimal.

Higher order bit

Lower order bit

(Example) DD RAM address “08”

AC

0

0

0

1

0

0

0

Hexadecimal

0

8

Hexadecimal