LSI 53C875A Manual De Usuario
3-14
Signal Descriptions
3.9 MAD Bus Programming
The MAD[7:0] pins, in addition to serving as the address/data bus for the
local memory interface, also are used to program power-up options for
the chip. A particular option is programmed allowing the internal
pull-down current sink to pull the pin LOW at reset or by connecting a
4.7 k
local memory interface, also are used to program power-up options for
the chip. A particular option is programmed allowing the internal
pull-down current sink to pull the pin LOW at reset or by connecting a
4.7 k
Ω
resistor between the appropriate MAD[x] pin and V
SS
. The
pull-down resistors require that HC or HCT external components are
used for the memory interface. The MAD[7:0] pins are sensed by internal
circuitry three PCI clock cycles after RST/ is deasserted.
used for the memory interface. The MAD[7:0] pins are sensed by internal
circuitry three PCI clock cycles after RST/ is deasserted.
•
MAD[7] Serial EEPROM programmable option. When allowed to be
pulled LOW by the internal pull-down current sink, the automatic data
download is enabled. When pulled HIGH by an external resistor, the
automatic data download is disabled. Please see
pulled LOW by the internal pull-down current sink, the automatic data
download is enabled. When pulled HIGH by an external resistor, the
automatic data download is disabled. Please see
in
and
and
registers in
for additional information.
•
MAD[6:4] Reserved and may be left floating.
•
The MAD[3:1] pins are used to set the size of the external expansion
ROM device attached. Encoding for these pins are listed in
ROM device attached. Encoding for these pins are listed in
(“0” indicates a pull-down resistor is attached, “1”
indicates a pull-up resistor is attached).
Table 3.15
Decode of MAD Pins
MAD[3:1]
Available Memory Space
000
16 Kbyte
001
32 Kbyte
010
64 Kbyte
011
128 Kbyte
100
256 Kbyte
101
512 Kbyte
110
1024 Kbyte
111
no external memory present