XC2200 Derivatives
System Units (Vol. 1 of 2)
Startup Configuration and Bootstrap Loading
User’s Manual
10-16
V2.1, 2008-08
SCFG/BSL, V1.3
10.6.2
Bootstrap Loaders using UART Protocol
XC2200 users have different possibilities to download code/data in which the
communication is based on UART (Universal Asynchronous Receiver and Transmitter)
protocol.
10.6.2.1 Standard UART Bootstrap Loader
The standard UART bootstrap loader transfers program code/data via channel 0 of
USIC0 (U0C0) into the PSRAM. The U0C0 receiver is only enabled after the
identification byte has been transmitted. A half duplex connection to the host is,
therefore, sufficient to feed the BSL.
Data is transferred from the external host to the XC2200 using asynchronous eight-bit
data frames without parity (1 start bit, 1 stop bit). The number of data bytes to be received
in standard UART boot mode is fixed to 32 bytes, which allows up to 16 two-byte
instructions.
Figure 10-2 Bootstrap Loader Sequence
The XC2200 scans the RxD line to receive a zero byte after entering UART BSL mode
and the respective initialization. The zero byte is considered as containing one start bit,
eight 0 data bits and one stop bit. From the duration of this zero byte it calculates the
corresponding baudrate factor with respect to the current CPU clock, initializes the serial
interface U0C0 accordingly and switches pin TxD to output. Using this baudrate, an
identification byte (D5
H
) is returned to the host that provides the loaded data.
mc_bsl_x2k.vsd
Reset
CONFIG.
PINS
RxD
TxD
CSP:IP
32 bytes
User Software
Internal BSL-Routine