© 2000 Scenix Semiconductor, Inc. All rights reserved. 51 SX User’s Manual Rev. 3.1 www.scenix.com Chapter 2 Architecture Table 2-10  FUSEX Word Register Configuration Bits for SX18/20/28AC & SX18/20/28AC75 Option Bits Description PINS Selects the number of pins. IRCTRIM2:
IRCTRIM Internal RC Oscillator Trim. This 3-bit field adjusts the operation of the internal
RC oscillator to make it operate within the target frequency range of 4.0 MHz
(typical) plus or minus 8%. Parts are shipped from the factory untrimmed. The
device relies on the programming tool to provide the trimming function.
000b = minimum frequency
111b = maximum frequency OPTIONX/
STACKX OPTION Register Extension and Stack Extension. Set to 1 to disable the pro-
grammability of bit 6 and bit 7 in the OPTION register, the RTW and RTE_IE
bits (in other words, to force these two bits to 1); and to limit the program stack
size to two locations. Clear to 0 to enable programming of the RTW and RTE_IE
bits in the OPTION register, and to extend the stack size to eight locations. CF Carry bit Input. Set to 1 to ignore the carry bit as an input to addition and subtrac-
tion operations. Clear to 0 to add the carry bit into all addition operations (ADD
fr,W means fr = fr + W + C); and to subtract the complement of the carry bit from
all subtraction operations (SUB fr,W means fr = fr – W – /C). BOR1:
BOR0 Brown-Out Reset. The BOR1:BOR0 bits enable or disable the brown-out reset
function and set the brown-out threshold voltage as follows:
00 = 4.2V
01 = 2.6V
10 = 2.2V
11 = Disable Brown-Out Reset BORTRIM1:
BORTRIM0 Brown-Out trim bits (parts are shipped out of the factory untrimmed). BP1:
BP0 Configured Memory Size. These two factory-configured bits should not be
changed unless you want to reduce the configured amount of program memory in
the device. To do so, use one the following BP1:BP0 settings:
00 = 1 page, 1 bank
01 = 1 page, 2 banks
10 = 4 pages, 4 banks
11 = 4 pages, 8 banks (default)