C8051T620/1/6/7 & C8051T320/1/2/3
268
Rev. 1.2
29. Programmable Counter Array
The Programmable Counter Array (PCA0) provides enhanced timer functionality while requiring less CPU
intervention than the standard 8051 counter/timers. The PCA consists of a dedicated 16-bit counter/timer
and five 16-bit capture/compare modules. Each capture/compare module has its own associated I/O line
(CEXn) which is routed through the Crossbar to Port I/O when enabled. The counter/timer is driven by a
programmable timebase that can select between six sources: system clock, system clock divided by four,
system clock divided by twelve, the external oscillator clock source divided by 8, Timer 0 overflows, or an
external clock signal on the ECI input pin. Each capture/compare module may be configured to operate
independently in one of six modes: Edge-Triggered Capture, Software Timer, High-Speed Output, Fre-
quency Output, 8 to 11-Bit PWM, or 16-Bit PWM (each mode is described in Section
“29.3. Capture/Compare Modules” on page 271). The external oscillator clock option is ideal for real-time
clock (RTC) functionality, allowing the PCA to be clocked by a precision external oscillator while the inter-
nal oscillator drives the system clock. The PCA is configured and controlled through the system controller's
Special Function Registers. The PCA block diagram is shown in Figure 29.1.
Important Note:
The PCA Module 4 may be used as a watchdog timer (WDT), and is enabled in this mode
following a system reset.
Access to certain PCA registers is restricted while WDT mode is enabled
.
See Section 29.4 for details.
Figure 29.1. PCA Block Diagram
16-Bit Counter/Timer
CE
X
1
EC
I
Digital Crossbar
CEX2
CE
X
0
Port I/O
Capture/Compare
Module 1
Capture/Compare
Module 0
Capture/Compare
Module 2
PCA
CLOCK
MUX
SYSCLK/12
SYSCLK/4
Timer 0 Overflow
ECI
SYSCLK
External Clock/8
Capture/Compare
Module 3
CEX3
Capture/Compare
Module 4 / WDT
CEX4