mc68hc05jb4p Freescale Semiconductor, Inc, mc68hc05jb4p Datasheet - Page 58

• Manufacturer Part Number: mc68hc05jb4p
• Description: Mc68hc705jb4 Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

GENERAL RELEASE SPECIFICATION
9.1
RESET
The basis of the 16-bit Timer is a 16-bit free-running counter which increases in
count with each internal bus clock cycle. The counter is the timing reference 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-
cific timer function allows full control of that function; however, an access of the
high byte inhibits that specific timer function until the low byte is also accessed.
Because the counter is 16 bits long and preceded by a fixed divide-by-four pres-
caler, the counter rolls over every 262,144 internal clock cycles. Timer resolution
with a 4MHz 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 flags can be read from the timer status register (TSR) located at
$0013.
TIMER REGISTERS (TMRH, TMRL)
The functional block diagram of the 16-bit free-running timer counter and timer
registers is shown in Figure 9-2. The timer registers include a transparent buffer
latch on the LSB of the 16-bit timer counter.
READ
TMRH
Figure 9-2. Programmable Timer Counter Block Diagram
($FFFC)
READ
$0012
Freescale Semiconductor, Inc.
TIMER CONTROL REG.
For More Information On This Product,
TMRH ($0018)
OVERFLOW (TOF)
Go to: www.freescale.com
February 24, 1999
LATCH
16-BIT COUNTER
16-BIT TIMER
TMRL ($0019)
TMR LSB
TIMER STATUS REG.
$0013
4
INTERNAL
INTERRUPT
READ
(f
TMRL
REQUEST
INTERNAL
CLOCK
OSC
TIMER
DATA
BUS
2)
REV