Pin Connection On Board; X1 And X2 Pins - NEC 78K0S/KA1+ User Manual

18.6 Pin Connection on Board

To write the flash memory on-board, connectors that connect the dedicated flash programmer must be provided on
the target system. First provide a function that selects the normal operation mode or flash memory programming
mode on the board.
When the flash memory programming mode is set, all the pins not used for programming the flash memory are in
the same status as immediately after reset. Therefore, if the external device does not recognize the state immediately
after reset, the pins must be processed as described below.
The state of the pins in the self programming mode is the same as that in the HALT mode.

18.6.1 X1 and X2 pins

The X1 and X2 pins are used as the serial interface of flash memory programming. Therefore, if the X1 and X2
pins are connected to an external device, a signal conflict occurs. To prevent the conflict of signals, isolate the
connection with the external device.
Perform the following processing (1) and (2) when on-board writing is performed with the resonator mounted, when
it is difficult to isolate the resonator, while a crystal or ceramic resonator is selected as the system clock.
(1) Mount the minimum-possible test pads between the device and the resonator, and connect the flash
programmer via the test pad. Keep the wiring as short as possible (refer to Figure 18-6 and Table 18-4).
(2) Set the oscillation frequency of the communication clock for writing using the GUI software of the dedicated
flash programmer. Research the series/parallel resonant and antiresonant frequencies of the resonator used,
and set the oscillation frequency so that it is outside the range of the resonant frequency ±10% (refer to Figure
18-7 and Table 18-5).
High-speed internal oscillation clock
External clock
Crystal/ceramic oscillation
clock
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CHAPTER 18 FLASH MEMORY
Figure 18-6. Example of Mounting Test Pads
V
SS
Table 18-4. Clock to Be Used and Mounting of Test Pads
Clock to Be Used
Before resonator is mounted
After resonator is mounted
User's Manual U16898EJ3V0UD
Test pad
X1 X2
Mounting of Test Pads
Not required
Required