Capture Operation - NEC UPD789426 Series User Manual

6.4.3 Capture operation

The capture operation consists of latching the count value of 16-bit timer register 90 (TM90) into a capture register
in synchronization with a capture trigger, and retaining the count value.
Set TMC90 as shown in Figure 6-9 to allow 16-bit timer 90 to start the capture operation.
Figure 6-9. Settings of 16-Bit Timer Mode Control Register 90 for Capture Operation
TOD90 TOF90 CPT901 CPT900 TOC90 TCL901 TCL900 TOE90
−
TMC90 0/1
16-bit capture register 90 (TCP90) starts a capture operation after a CPT90 capture trigger edge is detected, and
latches and retains the count value of 16-bit timer register 90. The TCP90 fetches the count value within 2 clocks and
retains the count value until the next capture edge detection.
Table 6-3 and Figure 6-10 show the settings of the capture edge and the capture operation timing, respectively.
CPT901 CPT900
0 0
0 1
1 0
1 1
Caution Because TCP90 is rewritten when a capture trigger edge is detected during TCP90 read, disable
the capture trigger edge detection during TCP90 read.
Figure 6-10. Capture Operation Timing (Both Edges of CPT90 Pin Are Specified)
Count clock
TM90 0000H
Count read buffer 0000H
TCP90
CPT90
130
CHAPTER 6 16-BIT TIMER 90
0/1 0/1 0/1 0/1
Table 6-3. Settings of Capture Edge
Capture operation prohibited
CPT90 pin rising edge
CPT90 pin falling edge
CPT90 pin both edges
0001H
0001H
Undefined
User's Manual U15075EJ2V1UD
0/1 0/1
Count clock selection
Capture edge selection (see Table 6-3)
Capture Edge Selection
N
N
N
Capture start
Capture edge detection
M 1 M
M
M
Capture start
Capture edge detection