参数资料
型号: ST72611F1M1
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDSO20
封装: 0.300 INCH, PLASTIC, SOP-20
文件页数: 28/77页
文件大小: 1178K
代理商: ST72611F1M1
ST7261
34/77
9.2 TIMEBASE UNIT (TBU)
9.2.1 Introduction
The Timebase unit (TBU) can be used to generate
periodic interrupts.
9.2.2 Main Features
I 8-bit upcounter
I Programmable prescaler
I Period between interrupts: max. 8.1ms (at 8
MHz fCPU)
I Maskable interrupt
9.2.3 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.
9.2.4 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 25. TBU Block Diagram
TBU 8-BIT UPCOUNTER (TBUCV REGISTER)
INTERRUPT REQUEST
TBU PRESCALER
fCPU
TBUCSR REGISTER
PR1
PR0
PR2
TCEN
ITE
OVF
MSB
LSB
0
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