Panasonic MN101C77C User Manual

Chapter 18 Flash EEPROM

XVIII - 18

Onboard Serial Interface Programming Mode

To connect resistors in series with communication pins (NRST, P53, P54)

When resistors are connected in series with communication pins, signal spectrum speed drops

affected by the load capacity. To ensure effecting reliable communication, the required time in

which the operating voltage reaches to 63% of the time constant must be shorter than 1/8 of

communication cycle. For example, the maximum resistor value, R

sMax

, derived from following

formula is 208

(at load capacity is 50 pF, communication cycle is12 MHz).

8 X Communication frequency X Load capacity

Large resistors can be connected in series with communication pins by lowering the communica-

tion speed. The resistor value should be smaller than 1/10 of the pull-up resistors.

Open-drain output through writer's communication pin (P53, P54)

During open-drain output through writer's communication pin, signal spectrum speed drops af-

fected by the pull-up resistors and the load capacity. To ensure effecting reliable communication,

the required time in which the operating voltage reaches to 63% of the time constant must be

shorter than 1/8 of communication cycle. The maximum communication cycle derived from foll-

owing formula is 1.38 MHz (at load capacity is 50 pF, pull-up resistor is 1.8 k

8 X Pull-up resistor (RupMin) X Load capacity

The communication frequency needs to be lowered for open-drain output, therefore, select push-

pull output, if possible.

sMax

Max