Philips Semiconductors Preliminary data
P89C51RA2/RB2/RC2/RD2xx80C51 8-bit Flash microcontroller family
8KB/16KB/32KB/64KB ISP/IAP Flash with 512B/512B/512B/1KB RAM
2002 Jul 18
34
Programmable Counter Array (PCA)
The Programmable Counter Array available on the
P89C51RA2/RB2/RC2/RD2xx is a special 16-bit Timer that has five
16-bit capture/compare modules associated with it. Each of the
modules can be programmed to operate in one of four modes: rising
and/or falling edge capture, software timer, high-speed output, or
pulse width modulator. Each module has a pin associated with it in
port 1. Module 0 is connected to P1.3 (CEX0), module 1 to P1.4
(CEX1), etc. The basic PCA configuration is shown in Figure 25.
The PCA timer is a common time base for all five modules and can
be programmed to run at: 1/6 the oscillator frequency, 1/2 the
oscillator frequency, the Timer 0 overflow, or the input on the ECI pin
(P1.2). The timer count source is determined from the CPS1 and
CPS0 bits in the CMOD SFR as follows (see Figure 28):
CPS1 CPS0 PCA Timer Count Source
0 0 1/6 oscillator frequency (6-clock mode);
1/12 oscillator frequency (12-clock mode)
0 1 1/2 oscillator frequency (6-clock mode);
1/4 oscillator frequency (12-clock mode)
1 0 Timer 0 overflow
1 1 External Input at ECI pin
In the CMOD SFR are three additional bits associated with the PCA.
They are CIDL which allows the PCA to stop during idle mode,
WDTE which enables or disables the watchdog function on
module 4, and ECF which when set causes an interrupt and the
PCA overflow flag CF (in the CCON SFR) to be set when the PCA
timer overflows. These functions are shown in Figure 26.
The watchdog timer function is implemented in module 4 (see
Figure 35).
The CCON SFR contains the run control bit for the PCA and the
flags for the PCA timer (CF) and each module (refer to Figure 29).
To run the PCA the CR bit (CCON.6) must be set by software. The
PCA is shut off by clearing this bit. The CF bit (CCON.7) is set when
the PCA counter overflows and an interrupt will be generated if the
ECF bit in the CMOD register is set, The CF bit can only be cleared
by software. Bits 0 through 4 of the CCON register are the flags for
the modules (bit 0 for module 0, bit 1 for module 1, etc.) and are set
by hardware when either a match or a capture occurs. These flags
also can only be cleared by software. The PCA interrupt system
shown in Figure 27.
Each module in the PCA has a special function register associated
with it. These registers are: CCAPM0 for module 0, CCAPM1 for
module 1, etc. (see Figure 30). The registers contain the bits that
control the mode that each module will operate in. The ECCF bit
(CCAPMn.0 where n=0, 1, 2, 3, or 4 depending on the module)
enables the CCF flag in the CCON SFR to generate an interrupt
when a match or compare occurs in the associated module. PWM
(CCAPMn.1) enables the pulse width modulation mode. The TOG
bit (CCAPMn.2) when set causes the CEX output associated with
the module to toggle when there is a match between the PCA
counter and the module’s capture/compare register. The match bit
MAT (CCAPMn.3) when set will cause the CCFn bit in the CCON
register to be set when there is a match between the PCA counter
and the module’s capture/compare register.
The next two bits CAPN (CCAPMn.4) and CAPP (CCAPMn.5)
determine the edge that a capture input will be active on. The CAPN
bit enables the negative edge, and the CAPP bit enables the positive
edge. If both bits are set both edges will be enabled and a capture will
occur for either transition. The last bit in the register ECOM
(CCAPMn.6) when set enables the comparator function. Figure 31
shows the CCAPMn settings for the various PCA functions.
There are two additional registers associated with each of the PCA
modules. They are CCAPnH and CCAPnL and these are the
registers that store the 16-bit count when a capture occurs or a
compare should occur. When a module is used in the PWM mode
these registers are used to control the duty cycle of the output.
MODULE FUNCTIONS:
16-BIT CAPTURE
16-BIT TIMER
16-BIT HIGH SPEED OUTPUT
8-BIT PWM
WATCHDOG TIMER (MODULE 4 ONLY)
MODULE 0
MODULE 1
MODULE 2
MODULE 3
MODULE 4
P1.3/CEX0
P1.4/CEX1
P1.5/CEX2
P1.6/CEX3
P1.7/CEX4
16 BITS
PCA TIMER/COUNTER
TIME BASE FOR PCA MODULES
16 BITS
SU00032
Figure 25. Programmable Counter Array (PCA)
