Journeys

Motorola S-Record Format

Note: The following description of Motorola S-records was found a number of years ago on the man pages of a UNIX system.

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.

S-record general format 


+-------------------//------------------//-----------------------+
| 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 converted to a hexadecimal value, contain the count of remaining character pairs in the record
address
A char [ 4, 6, or 8 ] field. These characters, when grouped and converted to a hexadecimal value, contain 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 converted to hexadecimal values, contain the memory loadable data or descriptive information
checksum
A char [ 2 ] field. These characters, when paired and converted to a hexadecimal value, contain 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.

S-record Types

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
mname
A char [ 20 ] subfield that is the module name
ver
A char [ 2 ] subfield that is the version number
rev
A char [ 2 ] subfield that is the revision number
description
A char [ 0 - 36 ] subfield that 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 intrepreted as a 2-byte address. The data field is composed of memory loadable data
S2
The type of record field is 'S2' (0x5332). The address field is intrepreted as a 3-byte address. The data field is composed of memory loadable data
S3
The type of record field is 'S3' (0x5333). The address field is intrepreted as a 4-byte address. The data field is composed of memory loadable data
S4
No definition supplied
S5
The type of record field is 'S5' (0x5335). The address field is intrepreted as a 2-byte value and contains the count of S1, S2, and S3 records previously transmitted. There is no data field
S6
No definition supplied
S7
The type of record field is 'S7' (0x5337). The address field contains the starting execution address and is intrepreted as 4-byte 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 intrepreted as 3-byte 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 intrepreted as 2-byte address. There is no data field

S-record 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 composed of:

The first S1 record is composed of:

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 composed of:

The S9 record is composed of:

Instructor Notes

There isn't any evidence that Motorola ever has made use of the header information within the data field of the S0 record, as described above. This must have been used by some third party vendors.

This 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.