Operating Modes
9
-12
DSP56303 User’s Manual
9.3.1.4 Timer Event Counter (Mode 3)
In Mode 3, the timer counts external events and issues an interrupt (if interrupt enable bits are
set) when the timer counts a preset number of events. The timer clock signal can be taken
from either the TIO input signal or the prescaler clock output. If an external clock is used, it
must be internally synchronized to the internal clock, and its frequency must be less than the
DSP56303 internal operating frequency divided by 4. The value of the TCSR[INV] bit
determines whether low-to-high (0 to 1) transitions or high-to-low (1 to 0) transitions
increment the counter. If the INV bit is set, high-to-low transitions increment the counter. If
the INV bit is cleared, low-to-high transitions increment the counter.
When the counter matches the value contained in the TCPR, TCSR[TCF] is set and a compare
interrupt is generated if the TCSR[TCIE] bit is set. If the TCSR[TRM] bit is set, the counter is
loaded with the value of the TLR when the next timer clock is received, and the count is
resumed. If the TCSR[TRM] bit is cleared, the counter continues to increment on each timer
clock. This process repeats until the timer is disabled.
Bit Settings
Mode Characteristics
TC3
TC2
TC1
TC0
Mode
Name
Function
TIO
Clock
0
0
1
1
3
Event Counter
Timer
Input
External
Figure 9-9. Event Counter Mode, TRM = 1
Mode 3 (internal clock): TRM = 1
N = write preload
M = write compare
TE
Clock
(TIO pin or prescale CLK)
TLR
TCPR
TCF (Compare Interrupt if TCIE = 1)
Counter (TCR)
first event
M
0
N
N + 1
M
N
N + 1
N
interrupts every
M - N clock
periods
if clock source
is from TIO pin,
TIO < 4
NOTE: If INV = 1, counter is clocked on 1-to-0 clock transitions, instead of 0-to-1 transitions.
Summary of Contents for DSP56303
Page 1: ...DSP56303 User s Manual 24 Bit Digital Signal Processor DSP56303UM AD Revision 1 January 2001 ...
Page 52: ...JTAG OnCE Interface 2 22 DSP56303 User s Manual ...
Page 114: ...General Purpose Input Output GPIO 5 10 DSP56303 User s Manual ...
Page 212: ...GPIO Signals and Registers 8 26 DSP56303 User s Manual ...
Page 268: ...Interrupt Equates A 22 DSP56303 User s Manual ...
Page 306: ...Programming Sheets B 38 DSP56303 User s Manual ...
Page 320: ...Index 14 DSP56303 User s Manual ...