Maxim Integrated Secure Microcontroller - Manual (Page 114)

Secure Microcontroller User’s Guide
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13.5 Mode 3
When Timer 0 is selected for operation in Mode 3, both TH0 and TL0 are configured independently as an
8-bit timer/counter and as an 8-bit timer.
Figure 13-3 illustrates the function of Timer 0 for Mode 3
operation.
For Timer 0 in Mode 3, TL0 becomes an 8-bit timer/counter that is controlled by the Timer 0 control bits
(TR0 and TF0) in the TMOD and TCON registers. TL0’s count input may be assigned to either the
12t
CLK
signal or to the external T0 pin through C/
T for Timer 0. In addition, the count input may be gated
as a function of the
INT0 pin using Timer 0’s GATE bit in TMOD.
TH0 becomes an 8-bit timer when Mode 3 is selected for Timer 0. TH0’s input can only be the 12t
CLK
signal. TR1 and TF1 are assigned for use with TH0 as is the interrupt for Timer 1, which will be
generated when TH0 overflows from all 1s.
When Timer 1 is selected for operation in Mode 3, it stops counting and holds its current value. This
action is the same as setting TR1 = 0. When Timer 0 is selected in Mode 3, Timer 1’s control bits are
stolen as described above. As a result, Timer 1’s functions are limited in this MODE. It is forced to
operate as a timer whose clock in-put is 12 t
CLK
and it cannot generate an interrupt on overflow. In
addition, it also cannot be used with the GATE function. However, it can be started and stopped by
switching it into or out of Mode 3 or it can be assigned as a baud rate generator for the serial port.