ADAM27P16 datasheet(13/39 Pages) ABOV

13 / 39 page

Page 12 of 38

2.2. Address Register

The following registers are used to address the ROM.

• Block address register (BA) :

Holds ROM's Block number (0~1h) to be addressed.

• Block buffer register (BB) :

Value of BB is loaded by an LBBY command when newly addressing a block.

Then it is shifted into the BA when rightly executing a branch instruction (BR)

and a subroutine call (CAL).

• Page address register (PA) :

Holds ROM's page number (0~Fh) to be addressed.

• Page buffer register (PB) :

Value of PB is loaded by an LPBI command when newly addressing a page.

Then it is shifted into the PA when rightly executing a branch instruction (BR)

and a subroutine call (CAL).

• Program counter (PC) :

Available for addressing word on each page.

• Stack register (SR) :

Stores returned-word address in the subroutine call mode.

ADAM27PXX

2. Architecture

2.2.1. Block address register and Block buffer register :

Address one of block #0 to #1 in the ROM by the 1-bit register.

Unlike the program counter, the block address register is not changed automatically.

To change the block address, take two steps such as

(1) writing in the block buffer what block to jump (execution of LBBY) and

(2) execution of BR or CAL, because instruction code is of eight bits so that block

can not be specified at the same time.

In case a return instruction (RTN) is executed within the subroutine that has been

called in the other block, the block address will be changed at the same time.

ADAM27P16 Datasheet(PDF) 13 Page - ABOV Semiconductor Co., Ltd.