AT89C5122D-RDRUM datasheet(148/208 Pages) ATMEL

148 / 208 page

148

AT83R5122, AT8xC5122/23

4202F–SCR–07/2008

Mode 3 (Two 8-bit Timers)

Mode 3 configures Timer 0 so that registers TL0 and TH0 operate as 8-bit Timers (see

Figure 95). This mode is provided for applications requiring an additional 8-bit Timer or

Counter. TL0 uses the Timer 0 control bits C/T0# and GATE0 in the TMOD register, and

TR0 and TF0 in the TCON register in the normal manner. TH0 is locked into a Timer

function (counting FUART) and takes over use of the Timer 1 interrupt (TF1) and run con-

trol (TR1) bits. Thus, operation of Timer 1 is restricted when Timer 0 is in mode 3.

Figure 96 gives the autoreload period calculation formulas for both TF0 and TF1 flags.

Figure 95.

Timer/Counter 0 in Mode 3: Two 8-bit Counters

Figure 96.

Mode 3 Overflow Period Formula

Timer 1

Timer 1 is identical to Timer 0 except for Mode 3 which is a hold-count mode. The fol-

lowing comments help to understand the differences:

•

Timer 1 functions as either a Timer or an event Counter in three operating modes.

Figure 89 through Figure 93 show the logical configuration for modes 0, 1, and 2.

Mode 3 of Timer 1 is a hold-count mode.

•

Timer 1 is controlled by the four high-order bits of the TMOD register (see Table 89

on page 151) and bits 2, 3, 6 and 7 of the TCON register (see Table 88 on page

150). The TMOD register selects the method of Timer gating (GATE1), Timer or

Counter operation (C/T1#) and the operating mode (M11 and M01). The TCON

interrupt flag (IE1) and the interrupt type control bit (IT1).

•

Timer 1 can serve as the Baud Rate Generator for the Serial Port. Mode 2 is best

suited for this purpose.

•

For normal Timer operation (GATE1 = 0), setting TR1 allows TL1 to be incremented

by the selected input. Setting GATE1 and TR1 allows external pin INT1# to control

Timer operation.

•

Timer 1 overflow (count rolls over from all 1s to all 0s) sets the TF1 flag and

generates an interrupt request.

TR0

TCON.4

TF0

TCON.5

INT0#

GATE0

TMOD.3

Overflow

Timer 0

Interrupt

Request

C/T0#

TMOD.2

TL0

(8 bits)

TR1

TCON.6

TH0

(8 bits)

TF1

TCON.7

Overflow

Timer 1

Interrupt

Request

CK_T0

TF0PER =

FCK_T0

⋅ (256 – TL0)

TF1PER =

FCK_T0

⋅ (256 – TH0)

AT89C5122D-RDRUM 数据表(PDF) 148 Page - ATMEL Corporation

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