Rainbow Electronics T89C5115 - Manual (Page 50)

50
T89C5115
4128A–8051–04/02
Mode 2 (8-bit Timer with Auto-
Reload) Mode 2 configures Timer 0 as an 8-bit Timer (TL0 register) that automatically reloads
from TH0 register (see Figure 24). 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.
Figure 24. Timer/Counter x (x= 0 or 1) in Mode 2
Mode 3 (Two 8-bit Timers) Mode 3 configures Timer 0 such that registers TL0 and TH0 operate as separate 8-bit
Timers (see Figure 25). 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
PER
/6) and takes over use of the Timer 1 interrupt (TF1) and
run control (TR1) bits. Thus, operation of Timer 1 is restricted when Timer 0 is in mode
3.
Figure 25. Timer/Counter 0 in Mode 3: Two 8-bit Counters
TRx
TCON reg
TFx
TCON reg
0
1
GATEx
TMOD reg
Overflow
Timer x
Interrupt
Request
C/Tx#
TMOD reg
TLx
(8 bits)
THx
(8 bits)
INTx#
Tx
FTx
CLOCK
÷ 6
see section “Clock”
TR0
TCON.4
TF0
TCON.5
INT0#
0
1
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
T0
FTx
CLOCK
÷ 6
FTx
CLOCK
÷ 6
see section “Clock”