COP224C Datasheet, PDF(8/24 Page) National Semiconductor (TI) – Single-Chip 1k and 2k CMOS Microcontrollers

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COP224C Datasheet, PDF (8/24 Pages) National Semiconductor (TI) – Single-Chip 1k and 2k CMOS Microcontrollers

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Functional Description (Continued)

4 All successive transfer of control instructions and suc-

cessive LBIs have been completed (e g if the main

program is executing a JP instruction which transfers

program control to another JP instruction the interrupt

will not be acknowledged until the second JP instruc-

tion has been executed)

c Upon acknowledgement of an interrupt the skip logic

status is saved and later restored upon popping of the

stack For example if an interrupt occurs during the exe-

cution of ASC (Add with Carry Skip on Carry) instruction

which results in carry the skip logic status is saved and

program control is transferred to the interrupt servicing

routine at hex address 0FF At the end of the interrupt

routine a RET instruction is executed to pop the stack

and return program control to the instruction following the

original ASC At this time the skip logic is enabled and

skips this instruction because of the previous ASC carry

Subroutines should not be nested within the interrupt

service routine since their popping of the stack will en-

able any previously saved main program skips interfering

with the orderly execution of the interrupt routine

d The instruction at hex address 0FF must be a NOP

e An LEI instruction may be put immediately before the

RET instruction to re-enable interrupts

INITIALIZATION

The internal reset logic will initialize the device upon power-

up if the power supply rise time is less than 1 ms and if the

operating frequency at CKI is greater than 32 kHz other-

wise the external RC network shown in Figure 4 must be

connected to the RESET pin (the conditions in Figure 4

must be met) The RESET pin is configured as a Schmitt

trigger input If not used it should be connected to VCC

Initialization will occur whenever a logic ââ0ââ is applied to the

RESET input providing it stays low for at least three instruc-

tion cycle times

Note If CKI clock is less than 32 kHz the internal reset logic (option

29e1) MUST be disabled and the external RC circuit must be used

TL DD 8422â6

FIGURE 4 Power-Up Circuit

Upon initialization the PC register is cleared to 0 (ROM ad-

dress 0) and the A B C D EN IL T and G registers are

cleared The SKL latch is set thus enabling SK as a clock

output Data Memory (RAM) is not cleared upon initializa-

tion The first instruction at address 0 must be a CLRA

(clear A register)

TIMER

There are two modes selected by mask option

a Time-base counter In this mode the instruction cycle fre-

quency generated from CKI passes through a 2-bit divide-

by-4 prescaler The output of this prescaler increments

the 8-bit T counter thus providing a 10-bit timer The pre-

scaler is cleared during execution of a CAMT instruction

and on reset

For example using a 3 58 MHz crystal with a divide-by-16

option the instruction cycle frequency of 223 70 kHz in-

crements the 10-bit timer every 4 47 ms By presetting the

counter and detecting overflow accurate timeouts be-

tween 17 88 ms (4 counts) and 4 577 ms (1024 counts)

are possible Longer timeouts can be achieved by accu-

mulating under software control multiple overflows

b External event counter In this mode a low-going pulse

(ââ1ââ to ââ0ââ) at least 2 instruction cycles wide on the IN2

input will increment the 8-bit T counter

Note The IT instruction is not allowed in this mode

TL DD 8422 â 7

Crystal

Value

32 kHz

455 kHz

2 096 MHz

3 6 MHz

Crystal or Resonator

220k

Component Values

C1(pF) C2(pF)

20M

10M

6 â 36

RC Controlled Oscillator

Cycle

Time

30k

82 pF

6 â 18 ms

Note 15ksRs150k

50 pFsCs150 pF

VCC

t4 5V

FIGURE 5 Oscillator Component Values

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