ST7PSCR1E4M1/XXX View Datasheet(PDF) - STMicroelectronics

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Description

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ST7PSCR1E4M1/XXX

8-BIT LOW-POWER, FULL-SPEED USB MCU WITH 16K FLASH, 768 RAM, SMARTCARD I/F, TIMER

STMicroelectronics 

ST7SCR

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

s 8-bit upcounter

s Programmable prescaler

s Period between interrupts: max. 8.1ms (at 8

MHz fCPU )

s 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.

Figure 26. TBU Block Diagram

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

1

MSB

LSB

0

TBU 8-BIT UPCOUNTER (TBUCV REGISTER)

TBU PRESCALER

fCPU

TBU

0 0 OVF ITE TCEN PR2 PR1 PR0

TBUCSR REGISTER

INTERRUPT REQUEST

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