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TMP47C201P

CMOS 4-bit Microcontroller

Toshiba 

TMP47C101/201

(1) Stack

The stack provides the area in which the return

address is saved before a jump is performed to the

processing routine at the execution of a subroutine call

instruction or the acceptance of an interrupt. When a

subroutine call instruction is executed, the contents

(the return address) of the program counter are saved;

when an interrupt is accepted, the contents of the pro-

gram counter and flags are saved.

When returning from the processing routine, executing

the subroutine return instruction [RET] restores the

contents of the program counter from the stack; exe-

cuting the interrupt return instruction [RETI] restores

the contents of the program counter and flags.

usable.If an interrupt is accepted with location 4

already used, the user-processed data stored in

addresses 4CH through 4FH corresponding to the

location 3 area is lost.)

The SPW is not initialized by hardware, requiring to

write the initial value (the location with which the use of

the stack starts) by using the initialization routine. Nor-

mally, the initial value of “12” is used.

Example: To initialize the SPW (when the stack is

used from location 12)

LD A,#12 ;

ST A,0FFH

SPW←12

The stack consists of up to 15 levels (locations 0

(3) Data Counter (DC)

through 14) which are provided in the data memory

(addresses 40H through 7BH). Each location consists

of 4-word data memory. Locations 13 and 14 are

The data counter is a 12-bit register to specify the

address of the data table to be referenced in the pro-

shared with the count registers of the timer/counters

gram memory (ROM). Data table reference is per-

(TC1, TC2) to be described later.

formed by the table look-up instructions [LDL A, @DC]

and [LDH A, @DC +]. The data table may be located

The save/restore locations in the stack are determined

anywhere within the program memory address space.

by the stack pointer word (SPW). The SPW is automat-

ically decremented after save, and incremented before

The DC is assigned with a RAM address in unit of 4

restore.That is, the value of the SPW indicates the

bits. Therefore, the RAM manipulation instruction is

stack location number for the next save.

used to set the initial value or read the contents of the

DC.

(2) Stack Pointer Word (SPW)

Address 7FH (3FH for the 47C101) in the data memory

is called the stack pointer word, which identifies the

location in the stack to be accessed (save or restore).

Generally, location number 0 to 12 can be set to the

SPW, providing up to 13 levels of stack nesting. Loca-

tions 13 and 14 are shared with the timer/counters to

be described later; therefore, when the timer/counters

are not used, the stack area of up to 15 levels is avail-

able. Address 7FH is assigned to the SPW, so that the

contents of the SPW cannot be set “15” in any case.

Example: To set the DC to 380H.

LD HL,#07CH ; Sets RAM address of

DCL to HL register pair.

ST #0H,@HL+ ; DC←380H

ST #8H,@HL+

ST #3H,@HL+

The SPW is automatically updated when a subroutine

call is executed or an interrupt is accepted. However, if

it is used in excess of the stack area permitted by the

data memory allocating configuration, the user-pro-

cessed data may be lost.(For example, when the user-

processed data area is in an address range 00H

through 4FH, up to location 4 of the stacks are

Figure 2-7. Data Counter

8/32

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