BCT-ETX-C3-XXX
S
INGLE
B
OARD
C
OMPUTER
T
ROUBLESHOOTING
G
UIDE
P
ROGRAMMING THE
B
OARD
The board includes an EEPROM and a Watchdog, both of which are accessible either by using a special BIOS
function (Int. 50h) or by using the correct device driver for the operating system being used.
USER EEPROM
The EEPROM on the BCT-ETX-C3-XXX unit is a NM93C46 serially programmed device. It comprises
128 bytes of user programmable memory, organised as 64 x 16 bit words. The EEPROM does not have to
be completely erased before writing to a single location.
Before it can be used, the EEPROM must be enabled within the BIOS. The BIOS provides two functions to
simplify user access to the EEPROM memory, available through a software interrupt (INT 50h):
Write to Single EEPROM Location
Calling Registers:
AH = 03
BL = Location (0 – 63)
DX = Write data (16-bit value)
Perform INT 50h
Return Registers:
AH = 00, and Carry flag is clear if successful
AH = 02, and Carry flag is set if function valid but disabled
AH = FF, and Carry flag set if function failed
READ Single EEPROM Location
Calling Registers:
AH = 04
BL = Location (0 – 63)
Perform INT 50h
Return Registers:
DX = EEPROM Data
AH = 00, and Carry flag is clear if successful
AH = 02, and Carry flag is set if function valid but disabled
AH = FF, and Carry flag set if function failed
WATCHDOG FACILITY
BCT-ETX-C3-XXX includes a watchdog timer circuit, which may be used to monitor software or processor
hardware failure. The time-out period of the watchdog is fixed at 1200 milliseconds. The timer is enabled
or disabled by using the software interrupt at INT 50h.
The following code demonstrates the control of the watchdog timer.
Enable/Disable Watchdog
Calling Registers:
AH = 05
AL = 01 to enable, 00 to disable
Perform INT 50h.
Return Registers:
AH = 00, and Carry flag is clear if successful
AH = 02, and Carry flag is set if function valid but disabled
AH = FF, and Carry flag set if function failed
