AT89C51CC02CA-RATUM datasheet(60/156 Pages) ATMEL

60 / 156 page

AT/T89C51CC02

4126J–CAN–05/06

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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 generating

an interrupt request.

•

When Timer 0 is in mode 3, it uses Timer 1’s overflow flag (TF1) and run control bit

(TR1). For this situation, use Timer 1 only for applications that do not require an

interrupt (such as a Baud Rate Generator for the Serial Port) and switch Timer 1 in

and out of mode 3 to turn it off and on.

•

It is important to stop Timer/Counter before changing mode.

Mode 0 (13-bit Timer)

Mode 0 configures Timer 1 as a 13-bit Timer, which is set up as an 8-bit Timer (TH1 reg-

ister) with a modulo-32 prescaler implemented with the lower 5 bits of the TL1 register

(See Figure 24). The upper 3 bits of TL1 register are ignored. Prescaler overflow incre-

ments TH1 register.

Mode 1 (16-bit Timer)

Mode 1 configures Timer 1 as a 16-bit Timer with TH1 and TL1 registers connected in

cascade (See Figure 25). The selected input increments TL1 register.

Mode 2 (8-bit Timer with Auto-

Reload)

Mode 2 configures Timer 1 as an 8-bit Timer (TL1 register) with automatic reload from

TH1 register on overflow (See Figure 26). TL1 overflow sets TF1 flag in TCON register

and reloads TL1 with the contents of TH1, which is preset by software. The reload

leaves TH1 unchanged.

Mode 3 (Halt)

Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt

Timer 1 when TR1 run control bit is not available i.e. when Timer 0 is in mode 3.

Interrupt

Each Timer handles one interrupt source that is the timer overflow flag TF0 or TF1. This

flag is set every time an overflow occurs. Flags are cleared when vectoring to the Timer

interrupt routine. Interrupts are enabled by setting ETx bit in IEN0 register. This assumes

interrupts are globally enabled by setting EA bit in IEN0 register.

Figure 28. Timer Interrupt System

TF0

TCON.5

ET0

IEN0.1

Timer 0

Interrupt Request

TF1

TCON.7

ET1

IEN0.3

Timer 1

Interrupt Request

AT89C51CC02CA-RATUM Datasheet(PDF) 60 Page - ATMEL Corporation

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