SH79F166APSLASH044PR datasheet(48/113 Pages) SINOWEALTH

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SH79F166A

Mode2: 16 bit Auto-Reload Timer with T4 Edge Trig

Timer4 operates as 16-bit timer in Mode2. The TH4 register holds the high eight bits of the 16-bit counter/timer, TL4 holds the

low eight bits. As the 16-bit timer register increments and overflows from 0xFFFF to 0x0000, the timer overflow flag TF4

(T4CON.7) is set and the 16-bit value in timer load register are reloaded into timer counter register, and an interrupt will occur if

Timer4 interrupts is enabled. The T4CLKS bit (T4CON.0) is 0 always. Only the system clock is selected as Timer4 clock.

In Mode2, After Setting the TR4 bit (T4CON.1), Timer4 does not start counting but waits the trig signal (rising or falling edge

controlled by T4M[1:0]) from T4. An active trig signal will start the Timer4. When Timer 4 overflows from 0XFFFF to 0x0000, TF4

will be set, TH4 and TL4 will be reloaded from timer load register, and Timer4 holds and waits the next trig edge.

When Timer4 is working, an active trig signal maybe come, if TC bit equals 0, the trig signal will be ignored; if TC bit equals 1,

Timer4 will be re-trigged.

Setting TR4 does not force the timer to reset. The timer register should be loaded with the desired initial value before the timer

is enabled.

TF4

The Block Diagram of Mode 2 of Timer 4

TL4

TH4

Increment Mode

0:Switch Off

1:Switch On

16 bit Counter

Interrupt

Request

Overflow

Flag

TR4

System Clock

Prescaler

1,8,64,256

T4PS[1:0]

control

M2_en

TC4

control

: M2_en set to 1 when T4 edge trig, M2_en set to 0 when counter overflow

Note:

(1) When Timer4 is running (TR4 = 1) as a timer in the baud rate generator mode, TH4 or TL4 should not be written to. Because

a write might overlap a reload and cause write and/or reload errors. So, the timer 4 must be turned off (TR4 = 0) before

accessing the TH4 or TL4 registers.

(2) When Timer4 is used as a counter, the frequency of input signal of T4 pin must be less than half of system clock.

SH79F166AP/044PR Datasheet(PDF) 48 Page - SINOWEALTH Electronic Ltd