ST7SCR1E4 datasheet(42/102 Pages) STMICROELECTRONICS

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ST7SCR

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12.2 TIME BASE UNIT (TBU)

12.2.1 Introduction

The Timebase unit (TBU) can be used to generate

periodic interrupts.

12.2.2 Main Features

8-bit upcounter

Programmable prescaler

Period between interrupts: max. 8.1ms (at 8

MHz fCPU )

Maskable interrupt

12.2.3 Functional Description

The TBU operates as a free-running upcounter.

When the TCEN bit in the TBUCSR register is set

by software, counting starts at the current value of

the TBUCV register. The TBUCV register is incre-

mented at the clock rate output from the prescaler

selected by programming the PR[2:0] bits in the

TBUCSR register.

When the counter rolls over from FFh to 00h, the

OVF bit is set and an interrupt request is generat-

ed if ITE is set.

The user can write a value at any time in the

TBUCV register.

12.2.4 Programming Example

In this example, timer is required to generate an in-

terrupt after a delay of 1 ms.

Assuming that fCPU is 8 MHz and a prescaler divi-

sion factor of 256 will be programmed using the

PR[2:0] bits in the TBUCSR register, 1 ms = 32

TBU timer ticks.

In this case, the initial value to be loaded in the

TBUCV must be (256-32) = 224 (E0h).

ld A, E0h

ld TBUCV, A

; Initialize counter value

ld A 1Fh

;

ld TBUCSR, A

; Prescaler factor = 256,

; interrupt enable,

; TBU enable

Figure 26. TBU Block Diagram

TBU 8-BIT UPCOUNTER (TBUCV REGISTER)

INTERRUPT REQUEST

TBU PRESCALER

fCPU

TBUCSR REGISTER

PR1

PR0

PR2

TCEN

ITE

OVF

MSB

LSB

TBU

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