NAME¶
srec - Motorola S-record record and file format
DESCRIPTION¶
Motorola S-records are a form of simple ASCII encoding for binary
data. This format is commonly used for firmware uploads to GPSes, industrial
robots, and other kinds of microcontroller-driven hardware. It has several
convenient properties, including inspectability, easy editing with any text
editor, and checksumming for verification of transmission across noisy
serial lines.
An S-record file consists of a sequence of specially formatted
ASCII character strings. An S-record will be less than or equal to 78 bytes
in length.
The order of S-records within a file is of no significance and no
particular order may be assumed.
The general format of an S-record follows:
+-------------------//------------------//-----------------------+
| type | count | address | data | checksum |
+-------------------//------------------//-----------------------+
type
A char[2] field. These characters describe the type of
record (S0, S1, S2, S3, S5, S7, S8, or S9).
count
A char[2] field. These characters when paired and
interpreted as a big-endian hexadecimal integer, display the count of
remaining character pairs in the record.
address
A char[4,6, or 8] field. These characters grouped and
interpreted as a big-endian hexadecimal integer, display the address at which
the data field is to be loaded into memory. The length of the field depends on
the number of bytes necessary to hold the address. A 2-byte address uses 4
characters, a 3-byte address uses 6 characters, and a 4-byte address uses 8
characters.
data
A char [0-64] field. These characters when paired and
interpreted as hexadecimal values represent the memory loadable data or
descriptive information.
checksum
A char[2] field. These characters when paired and
interpreted as a big-endian hexadecimal integer display the least significant
byte of the ones complement of the sum of the byte values represented by the
pairs of characters making up the count, the address, and the data
fields.
Each record is terminated with a line feed. If any additional or
different record terminator(s) or delay characters are needed during
transmission to the target system it is the responsibility of the
transmitting program to provide them.
There are 9 record types, as follows:
S0
The type of record is 'S0' (0x5330). The address field is
unused and will be filled with zeros (0x0000). The header information within
the data field is divided into the following subfields.
1.mname is char[20] and is the module name.
2.ver is char[2] and is the version number.
3.rev is char[2] and is the revision number.
4.description is char[0-36] and is a text comment.
Each of the subfields is composed of ASCII bytes whose associated
characters, when paired, represent one byte hexadecimal values in the case
of the version and revision numbers, or represent the hexadecimal values of
the ASCII characters comprising the module name and description.
S1
The type of record field is 'S1' (0x5331). The address
field is interpreted as a 2-byte big-endian address. The data field is
composed of memory loadable data.
S2
The type of record field is 'S2' (0x5332). The address
field is interpreted as a 3-byte big-endian address. The data field is
composed of memory loadable data.
S3
The type of record field is 'S3' (0x5333). The address
field is interpreted as a 4-byte big-endian address. The data field is
composed of memory loadable data.
S5
The type of record field is 'S5' (0x5335). The address
field is interpreted as a 2-byte big-endian value and contains the count of
S1, S2, and S3 records previously transmitted. There is no data field.
S7
The type of record field is 'S7' (0x5337). The address
field contains the starting execution address and is interpreted as a 4-byte
big-endian address. There is no data field.
S8
The type of record field is 'S8' (0x5338). The address
field contains the starting execution address and is interpreted as a 3-byte
big-endian address. There is no data field.
S9
The type of record field is 'S9' (0x5339). The address
field contains the starting execution address and is interpreted as a 2-byte
big-endian address. There is no data field.
EXAMPLE¶
Shown below is a typical S-record format file.
S00600004844521B
S1130000285F245F2212226A000424290008237C2A
S11300100002000800082629001853812341001813
S113002041E900084E42234300182342000824A952
S107003000144ED492
S5030004F8
S9030000FC
The file consists of one S0 record, four S1 records, one S5 record
and an S9 record.
The S0 record is comprised as follows:
•S0 S-record type S0, indicating it is a header
record.
•06 Hexadecimal 06 (decimal 6), indicating that
six character pairs (or ASCII bytes) follow.
•00 00 Four character 2-byte address field, zeroes
in this example.
•48 44 52 ASCII H, D, and R -
"HDR".
•1B The checksum.
The first S1 record is comprised as follows:
•S1 S-record type S1, indicating it is a data
record to be loaded at a 2-byte address.
•13 Hexadecimal 13 (decimal 19), indicating that
nineteen character pairs, representing a 2 byte address, 16 bytes of binary
data, and a 1 byte checksum, follow.
•00 00 Four character 2-byte address field;
hexidecimal address 0x0000, where the data which follows is to be
loaded.
•28 5F 24 5F 22 12 22 6A 00 04 24 29 00 08 23 7C
Sixteen character pairs representing the actual binary data.
•2A The checksum.
The second and third S1 records each contain 0x13 (19) character
pairs and are ended with checksums of 13 and 52, respectively. The fourth S1
record contains 07 character pairs and has a checksum of 92.
The S5 record is comprised as follows:
•S5 S-record type S5, indicating it is a count
record indicating the number of S1 records
•03 Hexadecimal 03 (decimal 3), indicating that
three character pairs follow.
•00 04 Hexadecimal 0004 (decimal 4), indicating
that there are four data records previous to this record.
•F8 The checksum.
The S9 record is comprised as follows:
•S9 S-record type S9, indicating it is a
termination record.
•03 Hexadecimal 03 (decimal 3), indicating that
three character pairs follow.
•00 00 The address field, hexadecimal 0 (decimal
0) indicating the starting execution address.
•FC The checksum.
NOTES¶
•There isn't any evidence that Motorola ever made
use of the header information within the data field of the S0 record, as
described above. This may have been used by some third party vendors.
•The Unix manual page on S-records is the only
place that a 78-byte limit on total record length or 64-byte limit on data
length is documented. These values shouldn't be trusted for the general
case.
•The count field can have values in the range of
0x3 (2 bytes of address + 1 byte checksum = 3, a not very useful record) to
0xff; this is the count of remaining character pairs, including
checksum.
•If you write code to convert S-Records, you
should always assume that a record can be as long as 514 (decimal) characters
in length (255 * 2 = 510, plus 4 characters for the type and count fields),
plus any terminating character(s). That is, in establishing an input buffer in
C, you would declare it to be an array of 515 chars, thus leaving room for the
terminating null character.
AUTHOR¶
From an anonymous web page, itself claiming to have been derived
from an old Unix manual page. Now maintained by the GPSD project, which
added endianness clarifications.
