Power-On Configuration Options; Automatic Branch Generation; Power-On Configuration Pins And Options - LSI Symbios SYM53C040 Technical Manual

2.7 Power-On Configuration Options

Table 2.2

Power-On Configuration Pins and Options

Signal Name Function
AD[1:0]

Automatic branch generation

AD5 Serial ROM automatic download
A[10:8] Download configuration address See
2
A11 Download serial port select
1. The values of these pins are latched into the Power-On Configuration Registers (System registers
0xFF01, 0xFF03).
2.7.1 Automatic Branch Generation
The power-on configuration of the SYM53C040 can be customized for
different applications using the AD5, AD[1:0], and A[11:8] pins.
summarizes the functionality that is enabled or disabled by using pull-up
resistors on these pins.
At reset, the microcontroller core fetches its first instruction from address
0x0000. Because the interrupt vectors are mapped to locations 0x0003
through 0x0032, an unconditional jump instruction must be issued as the
first instruction fetched from address 0x0000. The SYM53C040 address
decode logic automatically generates this jump instruction when the
microcontroller core accesses address locations 0x0000 through 0x0002
during its initial instruction fetch, if automatic branch generation is
enabled. Three address destinations are possible for this initial automatic
jump, configurable by external pull-up resistors on the AD0 and AD1 pins.
The states of these pins are checked on chip reset. In the SYM53C040,
the AD0 and AD1 signal pins have internal pull-down resistors, so these
pins power-up deasserted if no external pull-up is used. They power-up
asserted with an external pull-up resistor. If an external pull-up resistor
is detected on either of these pins, the internal pull-down resistor will be
disabled to reduce power dissipation. The destination of the first
instruction jump is determined by the power-on values of the AD0 and
AD1 pins, as described in
Power-On Configuration Options
1
Pull-up Use
See Table 2.3.
Enable with external pull-up.
Table 2.4.
Pull-up resistor changes serial ROM download
from Two-Wire Serial port 0 to port 1.
Table 2.3.
Table 2.2
2-21