A251: SETTING THE ADDRESS OF CONFIG BYTES

Information in this article applies to:

• C251 All Versions

QUESTION

I'm using the 251 microcontroller with a 27C256 (32K EPROM) and I need to know where I should locate the configuration bytes in the START251.A51 startup code file.

ANSWER

The configuration bytes are located at FF:FFF8h and FF:FFF9h. However, since the 32K EPROM does not extend that high in memory, the config bytes must be located at the addresses read when FF:FFF8h and FF:FFF9h are asserted on the address bus.

In the 32K EPROM, these addresses are 7FF8h and 7FF9h. The code in START251.A51 should appear as follows:

$IF (CONFIGB)
CONFIG0         EQU     (WSA*20H)+(XALE*10H)+(RDRG*4)+(PAGM*2)+SRCM+080H
CONFIG1         EQU     (INTR*10H)+(EDF*8)+(WSB*2)+EMAP+0E0H

                CSEG    AT      07FF8H
                DB      CONFIG0         ; Config Byte 0
                DB      CONFIG1         ; Config Byte 1
$ENDIF

SEE ALSO

• C251: SETTING THE DEVICE CONFIGURATION BYTES
• A251: LOCATING STARTUP ROUTINES IN ECODE

Last Reviewed: Wednesday, February 23, 2005