C8051F581-IMR Silicon Labs, C8051F581-IMR Datasheet - Page 313

• Manufacturer Part Number: C8051F581-IMR
• Description: 8-bit Microcontrollers - MCU 50MIPS 128kB 8kB SPI
• Manufacturer: Silicon Labs

Specifications of C8051F581-IMR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

28.1. PCA0 Counter/Timer
The 16-bit PCA0 counter/timer consists of two 8-bit SFRs: PCA0L and PCA0H. PCA0H is the high byte
(MSB) of the 16-bit counter/timer and PCA0L is the low byte (LSB). Reading PCA0L automatically latches
the value of PCA0H into a “snapshot” register; the following PCA0H read accesses this “snapshot” register.
Reading the PCA0L Register first guarantees an accurate reading of the entire 16-bit PCA0 counter.
Reading PCA0H or PCA0L does not disturb the counter operation. The CPS2 – CPS0 bits in the PCA0MD
register select the timebase for the counter/timer as shown in Table 28.1.
When the counter/timer overflows from 0xFFFF to 0x0000, the Counter Overflow Flag (CF) in PCA0MD is
set to logic 1 and an interrupt request is generated if CF interrupts are enabled. Setting the ECF bit in
PCA0MD to logic 1 enables the CF flag to generate an interrupt request. The CF bit is not automatically
cleared by hardware when the CPU vectors to the interrupt service routine, and must be cleared by soft-
ware. Clearing the CIDL bit in the PCA0MD register allows the PCA0 to continue normal operation while
the CPU is in Idle mode.
SYSCLK/12
SYSCLK/4
Timer 0 Overflow
ECI
SYSCLK
External Clock/8
Timer 4 Overflow
Timer 5 Overflow
*Note: External oscillator source divided by 8 is synchronized with the system clock.
CPS2
0
0
0
0
1
1
1
1
C
D
L
I
W
D
E
T
PCA0MD
W
D
C
K
L
CPS1
C
P
S
2
000
001
010
011
100
101
110
111
C
P
S
1
0
0
1
1
0
0
1
1
C
P
S
0
E
C
F
Figure 28.2. PCA0 Counter/Timer Block Diagram
IDLE
CPS0
Table 28.1. PCA0 Timebase Input Options
C
F
0
1
0
1
0
1
0
1
C
R
PCA0CN
C
C
F
5
C
C
F
4
C
C
F
3
System clock divided by 12.
System clock divided by 4.
Timer 0 overflow.
High-to-low transitions on ECI (max rate = system clock divided
by 4).
System clock.
External oscillator source divided by 8.
Timer 4 Overflow.
Timer 5 Overflow.
C
C
F
2
C
C
F
1
C
C
F
0
0
1
Rev. 1.2
PCA0L
read
Snapshot
Register
PCA0H
Timebase
PCA0L
C8051F58x/F59x
*
To SFR Bus
To PCA0 Modules
Overflow
CF
To PCA0 Interrupt System
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