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XC2200 Derivatives
System Units (Vol. 1 of 2)
Startup Configuration and Bootstrap Loading
User’s Manual
10-23
V2.1, 2008-08
SCFG/BSL, V1.3
10.6.3
Synchronous Serial Channel Bootstrap Loader
The Synchronous Serial Channel (SSC) bootstrap loader transfers program code/data
from an external serial EEPROM via channel 0 of USIC0 (U0C0) into the PSRAM. The
XC2200 is the master, so no additional elements (except for the EEPROM) are required.
The SSC bootstrap loading is a convenient way for initial and basic (go/fail) testing
during software development - it allows many various code-versions to be easy started
on the target system by re-programming a serial EEPROM.
During SSC bootstrap loading data is transferred from the external EEPROM to the
XC2200 using synchronous eight-bit data frames with MSB first. The number of data
bytes to be received in SSC boot mode is user-selectable. The serial clock rate is set to
f
SYS
/10, which results in 1 MHz after a power reset.
Once SSC BSL mode is entered and the respective initialization done, the XC2200 first
reads the header from the first addresses (00...0) of the target EEPROM.
This header consists of two items:
•
The memory identification byte: D5
H
•
The data size field: 1 byte or 2 bytes, depending on the EEPROM’s addressing mode
(8-bit or 16-bit, see
)
If both items are valid the BSL enters a loop to read the number of bytes defined by the
data size field (maximum is FF
H
or FF00
H
, depending on the EEPROM) via U0C0.
These bytes are stored sequentially into PSRAM starting at location E0’0000
H
and are
then executed. Therefore, the size of the PSRAM in the respective derivative determines
the real maximum block size to be downloaded.
An invalid header (identification byte
≠
D5
H
, data size field = 0 or greater than
65280/FF00
H
) is indicated by toggling the CS line low 3 times. This helps debugging
during the system setup phase.