mc68hc05pl4b Freescale Semiconductor, Inc, mc68hc05pl4b Datasheet - Page 52

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

GENERAL RELEASE SPECIFICATION
9.1
9-2
RESET
The basis of the capture/compare Timer is a 16-bit free-running counter which
increases in count with each internal bus clock cycle. The counter is the timing ref-
erence for the input capture and output compare functions. The input capture and
output compare functions provide a means to latch the times at which external
events occur, to measure input waveforms, and to generate output waveforms and
timing delays. Software can read the value in the 16-bit free-running counter at
any time without affect the counter sequence.
Because of the 16-bit timer architecture, the I/O registers for the input capture and
output compare functions are pairs of 8-bit registers. Each register pair contains
the high and low byte of that function. Generally, accessing the low byte of a spe-
ci c timer function allo ws full control of that function; however, an access of the
high byte inhibits that speci c timer function until the lo w byte is also accessed.
Because the counter is 16 bits long and preceded by a x ed divide-by-four pres-
caler, the counter rolls over every 262,144 internal clock cycles. Timer resolution
with a 4 MHz crystal oscillator is 2 microsecond/count.
The interrupt capability, the input capture edge, and the output compare state are
controlled by the timer control register (TCR) located at $0012 and the status of
the interrupt ags can be read from the timer status register (TSR) located at
$0013.
TIMER REGISTERS (TMRH, TMRL)
The functional block diagram of the 16-bit free-running timer counter and timer
registers is shown in Figure 9-2. The timer registers include a transparent buffer
latch on the LSB of the 16-bit timer counter.
TMRH
READ
Figure 9-2. Timer Counter and Register Block Diagram
($FFFC)
READ
$0012
Freescale Semiconductor, Inc.
TIMER CONTROL REG.
For More Information On This Product,
16-BIT PROGRAMMABLE TIMER
TMRH ($0018)
OVERFLOW (TOF)
Go to: www.freescale.com
LATCH
16-BIT COUNTER
April 30, 1998
TMRL ($0019)
TMR LSB
TIMER STATUS REG.
$0013
4
INTERNAL
INTERRUPT
(XTAL 2)
READ
TMRL
REQUEST
INTERNAL
CLOCK
MC68HC05PL4
TIMER
DATA
BUS
REV 2.0