Typewriter User Manual

MOTOROLA MC68340 USER’S MANUAL 8- 3
I
M
B
MODULE CONFIGURATION REGISTER
INTERRUPT REGISTER
CONTROL REGISTER
STATUS REGISTER
PRELOAD 1 REGISTER
PRELOAD 2 REGISTER
(SYSTEM CLOCK)
CLOCK
MUX
16-BIT
C
OUNTE
R
CLOCK
LOGIC
COUNTER
CLOCK
MUX
8-BIT
P
RESCALE
R
SELECTED
C
LOCK
TIN
TGATE
TIMEOUT
16-BIT
C
OMPARATO
R
TOUT
COUNTER REGISTER
COMPARE REGISTER
TIMER
EXTERNAL
I
NTERFAC
E
Figure 8-2. Timer Functional Diagram
8.1.1.4 CLOCK SELECTION LOGIC. The clock selection logic consists of two
multiplexers that select the clocks applied to the prescaler and counter. The first
multiplexer (labeled clock logic in Figure 8-2) selects between the clock input to the timer
(TINx) or one-half the frequency of the system clock (CLKOUT). This output of the first
multiplexer (called selected clock) is applied to both the 8-bit prescaler and the second
multiplexer. The second multiplexer selects the clock for the 16-bit counter, which is either
the selected clock or the 8-bit prescaler output.
8.1.2 Internal Control Logic
The timer receives operation commands on the IMB and, in turn, issues appropriate
operation signals to the internal timer control logic. This mechanism allows the timer
registers to be accessed and programmed. Refer to 8.4 Register Description for
additional information.
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
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