mc68hc05pl4b Freescale Semiconductor, Inc, mc68hc05pl4b Datasheet - Page 63

• Manufacturer Part Number: mc68hc05pl4b
• Description: Low-cost Single-chip Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

10.1
MC68HC05PL4
REV 2.0
This section describes the 8-bit count down timer module.
OVERVIEW
As shown in Figure 10-1 this timer contains a single 8-bit software programmable
countdown timer counter with a 3-bit software control prescaler. The counter’s
value may be preset under software control and counts down to zero. When the
counter decrements to zero, the timer8 interrupt request bit (T8IF in T8CR) is set.
Then if the timer interrupt is enabled (T8IE in T8CR is set) and the I-bit of the con-
dition code register are is cleared, the processor receives an interrupt. After com-
pletion of the current instruction, the processor proceeds to store the appropriate
registers on the stack and then fetches the timer8 interrupt vector in order to begin
serving the interrupt.
To COP
Watchdog
Circuit
Bus Clock
Internal
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 10-1. Timer8 Block Diagram
8
8
Go to: www.freescale.com
Interrupt Circuit
SECTION 10
8-BIT TIMER
T8IF T8IFR T8IE
8
Overflow
April 30, 1998
Detect
Circuit
8-BIT TIMER
Timer8 Control and Status Register ($0D)
Timer8 Counter Register ($0E)
8-bit count-down timer counter
7-bit prescaler counter
T8EN PS2 PS1 PS0
8
GENERAL RELEASE SPECIFICATION
(8 to 1 MUX)
Prescaler
Select
Logic
10-1