Initialization
Initializing the Internal Registers
126
EPC User
’
s Manual Revision 1.05
Copyright 1997-2000, V3 Semiconductor Inc.
14.2.4
Initialization Using the Serial EEPROM interface
The EPC registers can also be initialized using the serial EEPROM interface. When using
this method, the EPC
“
downloads
”
the values for the first half of the 256-byte internal
register block from a serial EEPROM connected to the SCL and SDA pins. All register bits of
type
“
FRW
”
or
“
FR
”
for configuration registers from 00H to 7FH are written by the serial
EEPROM. Only bits of type
“
R
”
cannot be written.
Serial EEPROM initialization is useful in the following situations:
Systems without a local processor that are using the EPC as a stand alone bridge
Systems that cannot guarantee that the EPC can be initialized in a timely fashion by
the local processor
Systems which wish to eliminate an additional variable (e.g. during software debug)
The EPC uses a I
2
C-like interface to download from the serial EEPROM. The interface is
designed to work with 24C02 style serial EEPROMs. Table 23 shows serial EEPROMs
known to be compatible with this interface.
When the reset input (LRESET or PRST, as selected by RDIR) is de-asserted, the SDA pin
is sampled at the rising edge of the reset input. If a serial PROM is present, the SDA pin will
be pulled high by the external pull-up resistor. The detection of a high signal on SDA at the
rising edge of the reset input begins the serial download. Each byte is read from the
EEPROM sequentially, starting from 0H and ending at 7FH.
NOTE
: To prevent serial initialization for systems initializing from the PCI or local bus, YOU
MUST TIE SDA TO GROUND through a 1-2.2K ohm resistor. See Figure 64 for example
circuits.
14.2.4.1
Programming the Serial EEPROM
Programming of the serial EEPROM is straightforward on most commercial EPROM
programmers. Each byte in the 128-byte EEPROM is programmed with the value desired in
the corresponding byte in the EPC
’
s register map. Unused registers should be programmed
with 0H.
The EPC may be used to program the EEPROM in the target application. Direct control over
the state of the SCL and SDA pins is available through the SYSTEM register. The system
programmer must provide the proper signal timing for the serial EEPROM through software
emulation of the I
2
C-like protocol. Examples of source code for programming the I
2
C
protocol can be found on the World Wide Web by searching for I
2
C using one of the internet
search engines.
Table 23: Serial EEPROMs Known Compatible with the EPC
Manufacturer
Device
Atmel
24C02
Microchip
24C02A
Xicor
X24C02