A serial EEPROM(U1908) of 256K bytes is used for storage of the NAM information, authentication keys, phasing data, ESN, and memory. The EEPROM serial inter -

face to the microcontroller i s a standard SPI-compatible i nterface.

U1300 is a 64K x 16 low voltage, low power SRAM. U1300 uses a parallel interface bus.

U1200 is a 512K x 16 flash EPROM. U1200 uses a parallel interface bus.

The WP* line is used during EPROM flash con ditions. When the EPROM is not being flash ed, WP* is at a low state. This condition w ill switch Q1811 off, thus, allowing

the gate of Q1806 to be pulled high. A high state at th e gate of Q1806 will switch Q1806 off, thus, not allow ing WP* from U1200 to be pulled high by B+.

During flashing condi tions, WP* is pulled high. This condition will switch Q1811 on , allowing the voltage at the gate of Q1806 to drop. A lower voltage at the gate of

Q1806 will switch the transistor on. This condition will allow WP* from U1200 to be pulled high by B+.

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