Motorola DSP56301 - Manual (Page 280)

Operating Modes
9 -18 DSP56301 User’s Manual
9.3.2.3 Measurement Capture (Mode 6)
In Mode 6, the timer counts the number of clocks that elapse between when the timer starts
and when an external signal is received. At the first appropriate transition of the external
clock detected on the
TIO signal, TCSR[TCF] is set and, if the TCSR[TCIE] bit is set, a
compare interrupt is generated. The counter halts. The contents of the counter are loaded into
the TCR. The value of the TCR represents the delay between the setting of the TCSR[TE] bit
and the detection of the first clock edge signal on the
TIO signal. The value of the INV bit
determines whether a high-to-low (1 to 0) or low-to-high (0 to 1) transition of the external
clock signals the end of the timing period. If the INV bit is set, a high-to-low transition signals
the end of the timing period. If INV is cleared, a low-to-high transition signals the end of the
timing period.
Bit Settings Mode Characteristics
TC3 TC2 TC1 TC0 Mode Name Function TIO Clock
0 1 1 0 6 Capture Measurement Input Internal
Figure 9-15. Capture Measurement Mode, TRM = 0
Mode 6 (internal clock): TRM = 1
N = write preload
M = write compare
TE
Clock
(CLK/2 or prescale CLK)
TLR
TCR
Counter
first event
M
0 N N + 1 M N N + 1
N
Interrupt Service
reads TCR; delay
NOTE: If INV = 1, a 1-to-0 edge on TIO loads TCR with count and stops the counter.
TCF (Compare Interrupt if TCIE = 1)
TIO pin
delay being measured
= M - N clock
periods
Counter stops
counting; overflow
may occur before
capture (TOF = 1)