C8051F120DK Silicon Laboratories Inc, C8051F120DK Datasheet - Page 326

• Manufacturer Part Number: C8051F120DK
• Description: DEVKIT-F120/21/22/23/24/25/26/27
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F120DK

• Contents: Evaluation Board, Power Supply, USB Cables, Adapter and Documentation
• Processor To Be Evaluated: C8051F12x and C8051F13x
• Interface Type: USB
• Silicon Manufacturer: Silicon Labs
• Core Architecture: 8051
• Silicon Core Number: C8051F120
• Silicon Family Name: C8051F12x
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: C8051F120, 121, 122, 123, 124, 125, 126, 127
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1224

C8051F120/1/2/3/4/5/6/7
C8051F130/1/2/3
24.1. PCA Counter/Timer
The 16-bit PCA 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. Read-
ing PCA0H or PCA0L does not disturb the counter operation. The CPS2–CPS0 bits in the PCA0MD regis-
ter select the timebase for the counter/timer as shown in Table 24.1.
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 (Note: PCA0 interrupts must be globally enabled before CF interrupts are recognized. PCA0 inter-
rupts are globally enabled by setting the EA bit (IE.7) and the EPCA0 bit in EIE1 to logic 1). Clearing the
CIDL bit in the PCA0MD register allows the PCA to continue normal operation while the CPU is in Idle
mode.
326
*Note: External clock divided by 8 is synchronized with the system clock.
SYSCLK/12
SYSCLK/4
Timer 0 Overflow
ECI
SYSCLK
External Clock/8
CPS2
0
0
0
0
1
1
C
D
L
I
W
D
T
E
CPS1
PCA0MD
W
D
C
K
L
0
0
1
1
0
0
C
P
S
2
000
001
010
011
100
101
C
P
S
1
C
P
S
0
Figure 24.2. PCA Counter/Timer Block Diagram
E
C
F
CPS0
Table 24.1. PCA Timebase Input Options
0
1
0
1
0
1
IDLE
C
F
C
R
PCA0CN
C
C
F
5
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*
C
C
F
4
C
C
F
3
C
C
F
2
C
C
F
1
C
C
F
0
0
1
Rev. 1.4
PCA0L
read
Snapshot
Register
PCA0H
Timebase
PCA0L
To SFR Bus
To PCA Modules
Overflow
CF
To PCA Interrupt System