AT89C51SND1_14 Datasheet, PDF (8/25 Pages) ATMEL Corporation – Based on the Intel Hex-type Records

Physical Layer
Frame Description
The UART used to transmit information has the following configuration:
• Character: 8-bit data
• Parity: none
• Stop: 1 bit
• Flow control: none
• Baud rate: auto baud is performed by the bootloader to compute the baud rate
chosen by the host.
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 in Table 4.
Table 4. Intel Hex Type Frame
Record Mark ‘:’ Record length
1 byte
1 byte
Load Offset
2 bytes
Record Type
1 byte
Data or Info
n byte
Checksum
1 byte
• Record Mark:
– Record Mark is the start of frame. This field must contain “:”.
• Record length:
– Record length specifies the number of Bytes of information or data which
follows the Record Type field.
• 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.
• Record Type:
– Record Type specifies the command type. This field is used to interpret the
remaining information within the frame.
• Data/Info:
– Data/Info is a variable length field. It consists of zero or more Bytes encoded as
pairs of hexadecimal 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 hexadecimal digits to one Byte of binary, and include the Record Length
field to the last Byte of the Data/Info field inclusive. Therefore, the sum of all the
ASCII pairs in a record after converting to binary, from the Record Length field
to and the Checksum field inclusive, is zero.
8 AT89C51SND1 UART Bootloader
4241B–MP3–07/04