NEC PD754144 User Manual page 178

(6) Notes on application of carrier generator (reload)
To output a carrier to the PTO2 pin, the time required for the initial carrier to be generated deviates by up to
one carrier clock after reloading (the contents of the no return zero buffer flag (NRZB) are transferred to the
no return zero flag (NRZ) by occurrence of the interrupt of timer counter channel 1, and the contents of NRZ
are updated to "1").
This is because reloading is performed asynchronously to the carrier clock, as illustrated below in order to
hold constant the high-level period of the carrier.
<If delay after reloading is minimum>
NRZB 0
NRZ
TOUT F/F 0 1
Clock
PTO2
<If delay after reloading is maximum>
NRZB 0
NRZ
TOUT F/F 0 1
Clock
PTO2
178
CHAPTER 6 PERIPHERAL HARDWARE FUNCTION
Reloading by occurrence of interrupt
0
0
Reloading by occurrence of interrupt
0
0
User's Manual U10676EJ3V0UM
1
1
1 0
1
1
1 0
Delay of up to one
carrier clock occurs.
1 0
1 0