at89c51re2-slsem ATMEL Corporation, at89c51re2-slsem Datasheet - Page 71

• Manufacturer Part Number: at89c51re2-slsem
• Description: At89c51re2 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

Mode 2 (8-bit Timer with Auto-
Reload)
Figure 9. Timer/Counter x (x = 0 or 1) in Mode 2
Mode 3 (Two 8-bit Timers)
Figure 10. Timer/Counter 0 in Mode 3: Two 8-bit Counters
54
INT0#
See the “Clock” section
See the “Clock” section
INTx#
AT89C51RE2
CLOCK
CLOCK
CLOCK
T0
FTx
Tx
FTx
FTx
TMOD reg
GATEx
GATE0
TMOD.3
÷ 6
÷ 6
÷ 6
TMOD reg
TMOD.2
C/T0#
C/Tx#
Mode 2 configures Timer 0 as an 8-bit Timer (TL0 register) that automatically reloads
from TH0 register (see Figure 9). TL0 overflow sets TF0 flag in TCON register and
reloads TL0 with the contents of TH0, which is preset by software. When the interrupt
request is serviced, hardware clears TF0. The reload leaves TH0 unchanged. The next
reload value may be changed at any time by writing it to TH0 register.
Mode 3 configures Timer 0 such that registers TL0 and TH0 operate as separate 8-bit
Timers (see Figure 10). 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 TMOD reg-
ister, and TR0 and TF0 in TCON register in the normal manner. TH0 is locked into a
Timer function (counting F
run control (TR1) bits. Thus, operation of Timer 1 is restricted when Timer 0 is in mode
3.
0
1
0
1
TCON reg
TCON.4
TR0
TRx
TCON.6
TR1
PER
/6) and takes over use of the Timer 1 interrupt (TF1) and
(8 bits)
(8 bits)
(8 bits)
(8 bits)
TH0
THx
TLx
TL0
Overflow
Overflow
Overflow
TCON reg
TCON.5
TCON.7
TFx
TF0
TF1
Timer x
Interrupt
Request
Timer 0
Interrupt
Request
Timer 1
Interrupt
Request
7663B–8051–03/07