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4-5
DEVICE CONFIGURATION
4.4 CONFIGURATION BYTE LOCATION SELECTOR (UCON)
The Configuration Byte Location Selector (UCON) applies only to OTPROM and EPROM prod-
ucts. In conjunction with EA#, UCON specifies whether the configuration array is accessed from
on-chip memory or external memory.
If the UCON bit is clear (e.g., UCON=0), the configuration array is fetched from on-chip nonvol-
atile memory at addresses FF:FFF8H to FF:FFFFH. The configuration bytes are located at loca-
tions FF:FFF8H and FF:FFF9H.
If UCON is set (e.g., UCON=1), the state of the EA# pin at device reset determines whether the
configuration array is accessed from on-chip memory or external memory. If EA# is connected
to V
CC
, the configuration array is accessed from on-chip nonvolatile memory at addresses
FF:FFF8H through FF:FFFFH (same as for UCON=0). If EA# is connected to V
SS
, the configu-
ration array is obtained from external memory (e.g., a 27512 EPROM).