AT89C5132
12.3.2
Mode 1 (16-bit Timer)
Mode 1 configures Timer 0 as a 16-bit Timer with TH0 and TL0 registers connected in cascade
(see Figure 12-4). The selected input increments TL0 register. Figure 12-5 gives the overflow
period calculation formula when in timer mode.
Figure 12-4. Timer/Counter x (x = 0 or 1) in Mode 1
TIMx
CLOCK
Timer x
Interrupt
Request
÷ 6
0
1
Overflow
THx
(8 Bits)
TLx
(8 Bits)
TFx
TCON Reg
Tx
C/Tx#
TMOD Reg
INTx
GATEx
TMOD Reg
TRx
TCON Reg
Figure 12-5. Mode 1 Overflow Period Formula
6
⋅
(65536 – (THx, TLx))
FTIMx
TFxPER
=
12.3.3
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 Table 42). 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 12-7 gives the autoreload period calculation formula
when in timer mode.
Figure 12-6. Timer/Counter x (x = 0 or 1) in Mode 2
TIMx
CLOCK
Timer x
Interrupt
Request
÷ 6
0
1
Overflow
TLx
(8 Bits)
TFx
TCON Reg
Tx
C/Tx#
TMOD Reg
INTx
THx
(8 Bits)
GATEx
TMOD Reg
TRx
TCON Reg
Figure 12-7. Mode 2 Autoreload Period Formula
6
⋅
(256 – THx)
FTIMx
TFxPER
=
12.3.4
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 12-8). This mode is provided for applications requiring an additional 8-bit Timer or
51
4173E–USB–09/07
ATMEL [ ATMEL ]
