P87C554 NXP Semiconductors, P87C554 Datasheet - Page 19

• Manufacturer Part Number: P87C554
• Description: The P87C554 Single-Chip 8-Bit Microcontroller is manufactured inan advanced CMOS process and is a derivative of the 80C51microcontroller family
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Capture Logic: The four 16-bit capture registers that Timer T2 is
connected to are: CT0, CT1, CT2, and CT3. These registers are
loaded with the contents of Timer T2, and an interrupt is requested
upon receipt of the input signals CT0I, CT1I, CT2I, or CT3I. These
input signals are shared with port 1. The four interrupt flags are in
the Timer T2 interrupt register (TM2IR special function register). If
the capture facility is not required, these inputs can be regarded as
additional external interrupt inputs.
Using the capture control register CTCON (see Figure 14), these
inputs may capture on a rising edge, a falling edge, or on either a
rising or falling edge. The inputs are sampled during S1P1 of each
cycle. When a selected edge is detected, the contents of Timer T2
are captured at the end of the cycle.
Measuring Time Intervals Using Capture Registers: When a
recurring external event is represented in the form of rising or falling
edges on one of the four capture pins, the time between two events
2002 Mar 25
80C51 8-bit microcontroller – 12 clock operation
16K/512 OTP/RAM, 8 channel 10-bit A/D, I
capture/compare, high I/O
T2ER
f
RT2
osc
T2
off
STE
TG
TG
S
S
S
S
S
S
External reset
enable
1/12
RTE
R
R
R
R
R
R
T
T
CT0I
CT0
CTI0
INT
P4.0
P4.1
P4.2
P4.3
P4.4
P4.5
P4.6
P4.7
Prescaler
Figure 13. Block Diagram of Timer 2
I/O port 4
CT1I
2
C, PWM,
CT1
CTI1
INT
17
T2 Counter
S
R
T
TG =
can be measured using Timer T2 and a capture register. When an
event occurs, the contents of Timer T2 are copied into the relevant
capture register and an interrupt request is generated. The interrupt
service routine may then compute the interval time if it knows the
previous contents of Timer T2 when the last event occurred. With a
12 MHz oscillator, Timer T2 can be programmed to overflow every
524 ms. When event interval times are shorter than this, computing
the interval time is simple, and the interrupt service routine is short.
For longer interval times, the Timer T2 extension routine may be
used.
Compare Logic: Each time Timer T2 is incremented, the contents
of the three 16-bit compare registers CM0, CM1, and CM2 are
compared with the new counter value of Timer T2. When a match is
found, the corresponding interrupt flag in TM2IR is set at the end of
the following cycle. When a match with CM0 occurs, the controller
sets bits 0-5 of port 4 if the corresponding bits of the set enable
register STE are at logic 1.
=
=
=
set
reset
toggle
toggle status
CMO (S)
COMP
CT2I
8-bit overflow interrupt
16-bit overflow interrupt
CT2
T2 SFR address:
INT
CTI2
INT
CM1 (R)
COMP
TML2
TMH2
INT
=
=
CT3I
lower 8 bits
higher 8 bits
CT3
CM2 (T)
COMP
CTI3
INT
P87C554
Product data
SU00757
INT