' 1999 Scenix Semiconductor, Inc. All rights reserved. 3 www.scenix.com Table 2 FUSE Word Bits for SX18/20/28AC with Datecode yywwxx (old revisions) Option Bits Description TURBO Turbo Mode. Set to 1 for  compatible  mode, in which the instruction rate oper-
ates at one-fourth the oscillator clock rate. Set to 0 for the turbo mode, in which
the instruction rate is equal to the oscillator clock rate. SYNC Synchronous Input Mode (for turbo mode operation). Set to 1 to disable or clear
to 0 to enable synchronous inputs. OPTIONX OPTION Register Extension. Set to 1 to disable the programmability 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). Clear to 0 to enable programming of the RTW and RTE_IE
bits in the OPTION register. STACKX Stack Extension. Set to 1 to limit the stack size to two locations. Clear to 0 to
extend the stack size to eight locations. IRC Internal RC Oscillator. Set to 1 to disable the internal oscillator and have the
OSC1 and OSC2 pins operate as defined by the FOSC1:FOSC0 bits. Clear to 0 to
enable the internal oscillator, and to have the OSC1 pin floating and the OSC2
pin weakly pulled high. DIV2:DIV0 Internal RC Oscillator Divider. This field sets the divide-by factor for generating
the instruction clock from the internal oscillator when the internal oscillator is
enabled (IRC = 0). The nominal instruction rate is determined by DIV2:DIV0 as
follows:
000 = 4 MHz
001 = 2 MHz
010 = 1 MHz
011 = 500 kHz
100 = 250 kHz
101 = 125 kHz
110 = 62.5 kHz
111 = 31.25 kHz CP Code Protection. Set to 1 for no code protection. Clear to 0 for code protection.
With code protection, the program code and configuration registers read back as
scrambled data. This prevents reverse-engineering of your proprietary code and
configuration options. WDTE Watchdog timer enable. Set to 1 to enable the Watchdog timer. Clear to 0 to dis-
able the Watchdog timer. FOSC1:
FOSC0 External Oscillator Configuration. This field sets up the device to operate with a
particular type of external oscillator when the device is configured to operate
with an external oscillator (IRC = 1). The type of external oscillator is determined
by FOSC1:FOSC0 as follows:
00 = LP   low-power crystal
01 = XT   normal crystal
10 = HS   high-speed crystal
11 = RC network   OSC2 is weakly pulled high and no CLKOUT output