PIC18FXX20
15.1 Timer4 Operation
15.0 TIMER4 MODULE
Timer4 can be used as the PWM time-base for the
PWM mode of the CCP module. The TMR4 register is
readable and writable, and is cleared on any device
RESET. The input clock (FOSC/4) has a prescale option
of 1:1, 1:4 or 1:16, selected by control bits
T4CKPS1:T4CKPS0 (T4CON<1:0>). The match out-
put of TMR4 goes through a 4-bit postscaler (which
gives a 1:1 to 1:16 scaling inclusive) to generate a
TMR4 interrupt (latched in flag bit TMR4IF, (PIR3<3>)).
The prescaler and postscaler counters are cleared
when any of the following occurs:
• a write to the TMR4 register
• a write to the T4CON register
The Timer4 module timer has the following features:
• 8-bit timer (TMR4 register)
• 8-bit period register (PR4)
• Readable and writable (both registers)
• Software programmable prescaler (1:1, 1:4, 1:16)
• Software programmable postscaler (1:1 to 1:16)
• Interrupt on TMR4 match of PR4
Timer4 has a control register shown in Register 15-1.
Timer4 can be shut-off by clearing control bit, TMR4ON
(T4CON<2>), to minimize power consumption. The
prescaler and postscaler selection of Timer4 are also
controlled by this register. Figure 15-1 is a simplified
block diagram of the Timer4 module.
• any device RESET (Power-on Reset, MCLR
Reset, Watchdog Timer Reset, or Brown-out
Reset)
TMR4 is not cleared when T4CON is written.
REGISTER 15-1: T4CON: TIMER4 CONTROL REGISTER
U-0
—
bit 7
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
T4OUTPS3 T4OUTPS2 T4OUTPS1 T4OUTPS0 TMR4ON T4CKPS1 T4CKPS0
bit 0
bit 7
Unimplemented: Read as '0'
bit 6-3
T4OUTPS3:T4OUTPS0: Timer4 Output Postscale Select bits
0000= 1:1 Postscale
0001= 1:2 Postscale
•
•
•
1111= 1:16 Postscale
bit 2
TMR4ON: Timer4 On bit
1= Timer4 is on
0= Timer4 is off
bit 1-0
T4CKPS1:T4CKPS0: Timer4 Clock Prescale Select bits
00= Prescaler is 1
01= Prescaler is 4
1x= Prescaler is 16
Legend:
R = Readable bit
- n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
2003 Microchip Technology Inc.
Advance Information
DS39609A-page 147
MICROCHIP [ MICROCHIP ]
