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Table 2.3
External Pull-up Values for Automatic Branch Generation
External Pull-up on AD1/AD0
Pull-up/Pull-up
Pull-up/None
None/Pull-up
None/None
2.7.2 External Serial ROM Configuration
2.7.3 Serial ROM Chip Address
2-22
Address locations 0x0033 and 0x0000 correspond to the internal RAM.
Address locations 0x8000 and 0x4000 correspond to external memory
accesses. Using no external pull-up resistors on AD0 and AD1 disables
the automatic branch instruction generation, and the microcontroller
fetches its first instruction from address 0x0000. If automatic branch
generation is disabled, a branch instruction must be downloaded into
address 0x0000, using an external serial ROM. The power-on setting of
AD0 and AD1 can be read in the
register (0xFF01) bits 0 and 1, respectively.
The SYM53C040 can attempt to download firmware from a serial ROM
at power-on, through the Two-Wire Serial interface. The serial ROM
download is performed immediately at power-on or after a reset, and the
microcontroller will hold off from fetching its first instruction until the
download completes.
The initial ROM download will be skipped if no external pull-up is used
on the AD5 signal pin (the pin has an internal pull-down). If a pull-up is
detected on the AD5 signal pin, the download will be attempted and the
internal pull-down will be disabled to reduce power dissipation.
The chip address of the serial ROM to be used in the power-on download
can be defined by using pull-up resistors on the A8, A9, and A10 signal
pins. There are eight possible chip addresses for most popular Two-Wire
Serial EEPROM devices.
EEPROM device from which the SYM53C040 will attempt the initial
configuration download, based on the values of the A[10:8] signal pins.
Functional Description
First instruction Branch Destination
0x8000
0x4000
0x0033
Fetched from 0x0000
Power-On Configuration Zero (POC0)
Table 2.4
describes the address of the serial
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