9202 datasheet(55/175 Pages) STMICROELECTRONICS

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UPSD3254A, UPSD3254BV, UPSD3253B, UPSD3253BV

Mode 0. Putting either Timer into Mode 0 makes

it look like an 8048 Timer, which is an 8-bit Counter

with a divide-by-32 prescaler. Figure 22 shows the

Mode 0 operation as it applies to Timer 1.

In this mode, the Timer register is configured as a

13-bit register. As the count rolls over from all '1s'

to all '0s,' it sets the Timer Interrupt Flag TF1. The

counted input is enabled to the Timer when TR1 =

1 and either GATE = 0 or /INT1 = 1. (Setting GATE

= 1 allows the Timer to be controlled by external in-

put /INT1, to facilitate pulse width measurements).

TR1 is a control bit in the Special Function Regis-

ter TCON (TCON Control Register). GATE is in

TMOD.

The 13-bit register consists of all 8 bits of TH1 and

the lower 5 bits of TL1. The upper 3 bits of TL1 are

indeterminate and should be ignored. Setting the

run flag does not clear the registers.

Mode 0 operation is the same for the Timer 0 as

for Timer 1. Substitute TR0, TF0, and /INT0 for the

corresponding Timer 1 signals in Figure 22. There

are two different GATE Bits, one for Timer 1 and

one for Timer0.

Mode 1. Mode 1 is the same as Mode 0, except

that the Timer register is being run with all 16 bits.

Table 38. TMOD Register (TMOD)

Table 39. Description of the TMOD Bits

543210

Gate

C/T

Gate

C/T

Bit

Symbol

Timer

Function

7Gate

Timer1

Gating control when set. Timer/Counter 1 is enabled only while INT1 pin is High and

TR1 control pin is set. When cleared, Timer 1 is enabled whenever TR1 control bit is set

6C/T

Timer or Counter selector, cleared for timer operation (input from internal system clock);

set for counter operation (input from T1 input pin)

(M1,M0)=(0,0): 13-bit Timer/Counter, TH1, with TL1 as 5-bit prescaler

(M1,M0)=(0,1): 16-bit Timer/Counter. TH1 and TL1 are cascaded. There is no prescaler.

(M1,M0)=(1,0): 8-bit auto-reload Timer/Counter. TH1 holds a value which is to be

reloaded into TL1 each time it overflows

(M1,M0)=(1,1): Timer/Counter 1 stopped

4M0

3Gate

Timer0

Gating control when set. Timer/Counter 0 is enabled only while INT0 pin is High and

TR0 control pin is set. When cleared, Timer 0 is enabled whenever TR0 control bit is set

2C/T

Timer or Counter selector, cleared for timer operation (input from internal system clock);

set for counter operation (input from T0 input pin)

(M1,M0)=(0,0): 13-bit Timer/Counter, TH0, with TL0 as 5-bit prescaler

(M1,M0)=(0,1): 16-bit Timer/Counter. TH0 and TL0 are cascaded. There is no prescaler.

(M1,M0)=(1,0): 8-bit auto-reload Timer/Counter. TH0 holds a value which is to be

reloaded into TL0 each time it overflows

(M1,M0)=(1,1): TL0 is an 8-bit Timer/Counter controlled by the standard TImer 0 control

bits. TH0 is an 8-bit timer only controlled by Timer 1 control bits

0M0

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