srec_mos_tech - MOS Technology file format
The MOS Technology format allows binary files to be uploaded and downloaded
between between a computer system (such as a PC, Macintosh, or workstation)
and an emulator or evaluation board for microcontrollers and microprocessors.
Each line consists of 5 fields. These are the length field, address field, data
field, and the checksum. The lines always start with a semicolon (;)
- The record length field is a 2 character (1 byte) field
that specifies the number of data bytes in the record. Typically this is
24 or less.
- This is a 2‐byte address that specifies where the
data in the record is to be loaded into memory, big‐endian.
- The data field contains the executable code,
memory‐loadable data or descriptive information to be
- The checksum is an 2‐byte field that represents the
least significant two bytes of the the sum of the values represented by
the pairs of characters making up the record's length, address, and data
The final line should have a data length of zero, and the data line count in the
address field. The checksum is not the usual checksum, it is instead a repeat
of the data line count.
In general, binary data will expand in sized by approximately 2.54 times when
represented with this format.
Here is an example MOS Technology format file. It contains the data
“Hello, World” to be loaded at address 0.
Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,
2009, 2010, 2011 Peter Miller
program comes with ABSOLUTELY NO WARRANTY; for details use
the ' srec_cat -VERSion License
' command. This is free software and you
are welcome to redistribute it under certain conditions; for details use the '
srec_cat -VERSion License
(The following information is reproduced from
http://users.telenet.be/kim1‐6502/6502/usrman.html#F just in
case it vanishes from the Web.)
The paper tape LOAD and DUMP routines store and retrieve data in a specific
format designed to insure error free recovery. Each byte of data to be stored
is converted to two half bytes. The half bytes (whose possible values are 0 to
F HEX) are translated into their ASCII equivalents and written out onto paper
tape in this form.
Each record outputted begins with a “;” character (ASCII 3B) to
mark the start of a valid record. The next byte transmitted (18HEX) or (24
decimal) is the number of data bytes contained in the record. The record's
starting address High (1 byte, 2 characters), starting address Lo (1 byte, 2
characters), and data (24 bytes, 48 characters) follow. Each record is
terminated by the record's check‐sum (2 bytes, 4 characters), a
carriage return (ASCII 0D), line feed (ASCII 0A), and six “NULL”
characters (ASCII 00). (NULL characters cause a blank area on the paper tape.)
The last record transmitted has zero data bytes (indicated by ;00) The starting
address field is replaced by a four digit Hex number representing the total
number of data records contained in the transmission, followed by the records
usual check‐sum digits. An “XOFF” character ends the
During a “LOAD” all incoming data is ignored until a
“;” character is received. The receipt of non ASCII data or a
mismatch between a records calculated check‐sum and the
check‐sum read from tape will cause an error condition to be recognized
by KIM. The check‐sum is calculated by adding all data in the record
except the “;” character.
The paper tape format described is compatible with all other MOS Technology,
Inc. software support programs.