C8051F020/1/2/3
22.3.
Timer 4
Timer 4 is a 16-bit counter/timer formed by the two 8-bit SFRs: TL4 (low byte) and TH4 (high byte). As with
Timers 0 and 1, Timer 4 can use either the system clock or transitions on an external input pin (T4) as its clock
source. The Counter/Timer Select bit C/T4 bit (T4CON.1) selects the clock source for Timer 4. Clearing C/T4 selects
the system clock as the input for the timer (divided by either one or twelve as specified by the Timer Clock Select bit
T4M in CKCON). When C/T4 is set to 1, high-to-low transitions at the T4 input pin increment the counter/timer reg-
ister. Refer to
Section “17.1. Ports 0 through 3 and the Priority Crossbar Decoder” on page 163
for information
on selecting and configuring external I/O pins for digital peripherals.
Timer 4 offers capabilities not found in Timer 0 and Timer 1. It operates in one of three modes: 16-bit Counter/Timer
with Capture, 16-bit Counter/Timer with Auto-Reload or Baud Rate Generator Mode. Timer 4's operating mode is
selected by setting configuration bits in the Timer 4 Control register (T4CON). Below is a summary of the Timer 4
operating modes and the T4CON bits used to configure the counter/timer. Detailed descriptions of each mode follow.
RCLK1
0
0
0
1
1
X
TCLK1
0
0
1
0
1
X
CP/RL4
1
0
X
X
X
X
TR4
1
1
1
1
1
0
Mode
16-bit Counter/Timer with Capture
16-bit Counter/Timer with Auto-Reload
Baud Rate Generator for UART1
Baud Rate Generator for UART1
Baud Rate Generator for UART1
Off
Rev. 1.4
243
SILABS [ SILICON LABORATORIES ]
