MC68HC05V12 Datasheet, PDF (94/246 Pages) Freescale Semiconductor, Inc – HCMOS Microcontreller Unit

16-Bit Timer
Freescale Semiconductor, Inc.
HIGH LOW
BYTE BYTE
$16 OUTPUT
$17 COMPARE
REGISTER
INTERNAL BUS
INTERNAL
PROCESSOR
CLOCK
8-BIT
BUFFER
÷4
HIGH
BYTE
LOW
BYTE
16-BIT FREE-
RUNNING
COUNTER
$18
$19
COUNTER _$1A
ALTERNATE _$1B
REGISTER
HIGH LOW
BYTE BYTE
INPUT
CAPTURE
REGISTER
$14
$15
OUTPUT
COMPARE
CIRCUIT
OVERFLOW
DETECT
CIRCUIT
EDGE
DETECT
CIRCUIT
TIMER
STATUS
ICF OCF
TOF $13
REGISTER
INTERRUPT
CIRCUIT
DQ
CLK
OUTPUT
LEVEL C
REGISTER
TIMER ^RESET
ICIE OCIE TOIE IEDG OLVL _CONTROL
REGISTER
$12
OUTPUT
LEVEL
EDGE
INPUT
(TCMP) _(TCAP)
PB6 PB7
Figure 9-1. 16-Bit Timer Block Diagram
9.3 Timer Counter Registers $18−$19 and $1A−$1B
The key element in the programmable timer is a 16-bit, free-running
counter or counter register preceded by a prescaler that divides the
internal processor clock by four. The prescaler gives the timer a
resolution of 2.0 microseconds if the internal bus clock is 2.0 MHz. The
counter is incremented during the low portion of the internal bus clock.
Software can read the counter at any time without affecting its value.
The double-byte, free-running counter can be read from either of two
locations, $18–$19 (counter register) or $1A–$1B (counter alternate
register). A read from only the least significant byte (LSB) of the free-
running counter ($19, $1B) receives the count value at the time of the
read. If a read of the free-running counter or counter alternate register
Technical Data
16-Bit Timer
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MC68HC05V12 — Rev. 2.0