Rainbow-electronics ATAR862-8 User Manual download pdf (Page 16)

ATAR862-8

4589B–4BMCU–02/03

Figure 12. RAM Map

Registers The microcontroller has seven programmable registers and one condition code register

(see Figure 13).

Program Counter (PC) The program counter is a 12-bit register which contains the address of the next instruc-

tion to be fetched from the ROM. Instructions currently being executed are decoded in

the instruction decoder to determine the internal micro-operations. For linear code (no

calls or branches), the program counter is incremented with every instruction cycle. If a

branch-, call-, return-instruction or an interrupt is executed, the program counter is

loaded with a new address. The program counter is also used with the table instruction

to fetch 8-bit wide ROM constants.

Figure 13. Programming Mode l

RAM

FCh

00h

Autosleep

FFh

03h

04h

TOS-1

Expression

stack

Return

stack

Global

variables

RAM address register:

07h

(256 x 4-bit)

Global

variables

4-bit

TOS

TOS-1

TOS-2

Expression stack

Return stack

011

12-bit

TOS

CCR

Program counter

Return stack pointer

Expression stack pointer

RAM address register (X)

RAM address register (Y)

Top of stack register

Condition code register

Carry / borrow

Branch

Interrupt enable

Reserved

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 105 106

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Rainbow-electronics ATAR862-8 User Manual Page 16

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