Datasheet

102
4235K–8051–05/08
AT89C51RD2/ED2
24.7 ISP Protocol Description
24.7.1 Physical Layer
The UART used to transmit information has the following configuration:
• Character: 8-bit data
• Parity: none
• Stop: 2 bits
• Flow control: none
• Baudrate: autobaud is performed by the bootloader to compute the baudrate chosen by the
host.
24.7.2 Frame Description
The Serial Protocol is based on the Intel Hex-type records.
Intel Hex records consist of ASCII characters used to represent hexadecimal values and are
summarized below.
Figure 24-6. Intel Hex Type Frame
• Record Mark:
Record Mark is the start of frame. This field must contain ’:’.
• Reclen:
Reclen specifies the number of bytes of information or data which follows the Record Type field
of the record.
• Load Offset:
Load Offset specifies the 16-bit starting load offset of the data bytes, therefore this field is used
only for Data Program Record (see Section “ISP Commands Summary”).
• Record Type:
Record Type specifies the command type. This field is used to interpret the remaining informa-
tion within the frame. The encoding for all the current record types is described in Section “ISP
Commands Summary”.
• Data/Info:
Data/Info is a variable length field. It consists of zero or more bytes encoded as pairs of hexa-
decimal digits. The meaning of data depends on the Record Type.
• Checksum:
The two’s complement of the 8-bit bytes that result from converting each pair of ASCII hexadec-
imal digits to one byte of binary, and including the Reclen field to and including the last byte of
the Data/Info field. Therefore, the sum of all the ASCII pairs in a record after converting to
binary, from the Reclen field to and including the Checksum field, is zero.
Record
Record
Load
Data
Mark
’:’
Reclen
Offset
Type
or
Info
Checksum
1-byte
1-byte 2-bytes
1-byte
n-bytes 1-byte