Rainbow Electronics AT89LP216 - Manual (Page 29)

29
3621A–MICRO–6/06
AT89LP216 [Preliminary]
14.3 Mode 2 – 8-bit Auto-Reload Timer/Counter
Mode 2 configures the Timer register as an 8-bit Counter (TL1) with automatic reload, as shown
in
Figure 14-3 . Overflow from TL1 not only sets TF1, but also reloads TL1 with the contents of
TH1, which is preset by software. The reload leaves TH1 unchanged. Mode 2 operation is the
same for Timer/Counter 0.
Figure 14-3. Timer/Counter 1 Mode 2: 8-bit Auto-Reload
Note: RH1/RL1 are not required by Timer 1 during Mode 2 and may be used as temporary storage
registers.
14.4 Mode 3 – 8-bit Split Timer
Timer 1 in Mode 3 simply holds its count. The effect is the same as setting TR1 = 0. Timer 0 in
Mode 3 establishes TL0 and TH0 as two separate counters. The logic for Mode 3 on Timer 0 is
shown in
Figure 14-4 . TL0 uses the Timer 0 control bits: C/T, GATE, TR0, INT0, and TF0. TH0 is
locked into a timer function (counting machine cycles) and takes over the use of TR1 and TF1
from Timer 1. Thus, TH0 now controls the Timer 1 interrupt. While Timer 0 is in Mode 3, Timer 1
will still obey its settings in TMOD but cannot generate an interrupt.
Mode 3 is for applications requiring an extra 8-bit timer or counter. With Timer 0 in Mode 3, the
AT89LP216 can appear to have three Timer/Counters. When Timer 0 is in Mode 3, Timer 1 can
be turned on and off by switching it out of and into its own Mode 3. In this case, Timer 1 can still
be used by the serial port as a baud rate generator or in any application not requiring an
interrupt.
Figure 14-4. Timer/Counter 0 Mode 3: Two 8-bit Counters
Note: RH0/RL0 are not required by Timer 0 during Mode 3 and may be used as temporary storage
registers.
Mode 2: Time-out Period
256
TH
0 –
( )
Oscillator Frequency
------------------------------------------------------- TPS
1 +
( ) ×
=
OSC
T1 Pin
TR1
GATE
TF1
TL1
(8 Bits)
TH1
(8 Bits)
Control
Reload
Interrupt
INT0 Pin
C/T = 0
C/T = 1
÷TPS
Control
Interrupt
Control
Interrupt
(8 Bits)
(8 Bits)
C/T = 0
C/T =1
T0 Pin
GATE
INT0 Pin
÷TPS
÷TPS