Rainbow Electronics AT89C5122 - Manual (Page 151)

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AT8xC5122/23
4202E–SCR–06/06
• When Timer 0 is in mode 3, it uses Timer 1’s overflow flag (TF1) and run control bit
(TR1). For this situation, use Timer 1 only for applications that do not require an
interrupt (such as a Baud Rate Generator for the Serial Port) and switch Timer 1 in
and out of mode 3 to turn it off and on.
• It is important to stop the Timer/Counter before changing modes.
Mode 0 (13-bit Timer) Mode 0 configures Timer 1 as a 13-bit Timer, which is set up as an 8-bit Timer (TH1 reg-
ister) with a modulo-32 prescaler implemented with the lower 5 bits of the TL1 register
(see Figure 90). The upper 3 bits of TL1 register are ignored. Prescaler overflow incre-
ments the TH1 register.
Mode 1 (16-bit Timer) Mode 1 configures Timer 1 as a 16-bit Timer with TH1 and TL1 registers connected in
cascade (see Figure 92). The selected input increments the TL1 register.
Mode 2 (8-bit Timer with Auto-
Reload) Mode 2 configures Timer 1 as an 8-bit Timer (TL1 register) with automatic reload from
the TH1 register on overflow (see Figure 94). TL1 overflow sets the TF1 flag in the
TCON register and reloads TL1 with the contents of TH1, which is preset by the soft-
ware. The reload leaves TH1 unchanged.
Mode 3 (Halt) Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt
Timer 1 when the TR1 run control bit is not available i.e. when Timer 0 is in mode 3.