Tally T5023+ Programming Manual page 298

Length of the Transfer
The header can be used to determine the overall number of bytes to be loaded,
including the header itself.
The file header and the checksum can be used to determine that a file is valid:
Check sum calculation:
Sum of all 16-bit words = 0
Acknowledgment of a successful load process:
If the load process was completed successfully, the data ID is returned after 60s
max. (typically after 15s):
ESC ID
$MOD$ yymmdd rrvv BOOTPROM.FRM:
$MOD$ yymmdd rrvv CP15__437.FNT:
$MOD$ yymmdd rrvv 5023_STD.PAR;
The passbook and document printer will be booted again after this
acknowledgment if the firmware is available. During the reboot phase the
interface cannot be addressed for 10s max.
Problems during the load process:
If the loaded data is determined as not valid, the appropriate file header is
missing in the acknowledgment.
If the data transfer is interrupted for 60 seconds min. during the load process,
the file header is returned. The bootstrap loader resets to the home position. Any
data transferred is invalid, and the load process must be re-started.
Before any load command can be transferred, the system must switch the
Centronics interface card to the ECP mode (bi-directional). No data will be
processed in the compatible mode
288
Loadable Firmware/Character Genera-
T5023/5023+ - Programming Guide