mc68hc05j5ap Freescale Semiconductor, Inc, mc68hc05j5ap Datasheet - Page 62

• Manufacturer Part Number: mc68hc05j5ap
• Description: General Description The Mc68hc05j5a Is A Member Of The Low-cost High-performance M68hc05 Family Of 8-bit Microcontroller Units Mcus . The M68hc05 Family Is Based On The Customer-speci Ed Integrated Circuit Design Strategy. All Mcus In The Family
• Manufacturer: Freescale Semiconductor, Inc

GENERAL RELEASE SPECIFICATION
9-4
counter will not have any effect on the T1OF flag bit and Timer interrupts. The
alternate counter registers include a transparent buffer latch on the LSB of the 16-
bit timer counter.
The alternate counter registers (ACNTH, ACNTL) shown in Figure 9-5 are read-
only locations which contain the current high and low bytes of the 16-bit free-run-
ning counter. Writing to the alternate counter registers has no effect. Reset of the
device presets the timer counter to $FFFC.
The ACNTL latch is a transparent read of the LSB until the a read of the ACNTH
takes place. A read of the ACNTH latches the LSB into the ACNTL location until
the ACNTL is again read. The latched value remains fixed even if multiple reads of
the ACNTH take place before the next read of the ACNTL. Therefore, when read-
ing the MSB of the timer at ACNTH the LSB of the timer at ACNTL must also be
read to complete the read sequence.
During power-on-reset (POR), the counter is initialized to $FFFC and begins
counting after the oscillator start-up delay. Because the counter is 16 bits and pre-
ceded by a fixed divide-by-four prescaler, the value in the counter repeats every
262,144 internal bus clock cycles (524,288 oscillator cycles).
Reading the ACNTH and ACNTL in any order or any number of times does not
have any effect on the 16-bit free-running counter or the T1OF flag bit.
ACNTH
$001A
ACNTL
$001B
RESET
ACNTH
READ
reset:
reset:
W
W
R
R
Figure 9-5. Alternate Counter Registers (ACNTH, ACNTL)
($FFFC)
READ
BIT 7
Bit15
Figure 9-4. Alternate Counter Block Diagram
Bit7
1
1
Freescale Semiconductor, Inc.
For More Information On This Product,
BIT 6
Bit14
ACNTH ($1A)
Bit6
1
1
Go to: www.freescale.com
16-BIT COUNTER
LATCH
BIT 5
Bit13
Bit5
16-BIT TIMER
July 16, 1999
1
1
ACNTL ($1B)
BIT 4
Bit12
Bit4
TMR LSB
1
1
BIT 3
Bit11
Bit3
1
1
4
BIT 2
Bit10
Bit2
1
1
INTERNAL
INTERNAL
ACNTL
(f
READ
CLOCK
BIT 1
OSC
DATA
Bit9
Bit1
BUS
1
0
MC68HC05J5A
2)
REV 2.1
BIT 0
Bit8
Bit0
1
0