4 ' 1999 Scenix Semiconductor, Inc. All rights reserved. www.scenix.com Table 3 FUSE Word Bits for SX18/20/28AC with Datecode Axyywwxx (new revision) 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. 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. DIV1: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 DIV1:DIV0 as
follows:
00 = 4 MHz
01 = 1 MHz
10 = 128 kHz
11 = 32 kHz IFBD Internal Feedback Disable. If IRC = 1, and IFBD = 1, the crystal/resonator oscil-
lator can rely on the internal feedback resistor between the OSC1 and OSC2 pins.
If IFBD = 0, an external feedback resistor is required between the OSC1 and
OSC2 pins. 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. FOSC2:
FOSC0 External Oscillator Configuration. This combination of three register bits 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). Note that bit 5, the
DIV0/FOSC2 bit, operates as DIV0 with IRC=0, or as FOSC2 with IRC=1. The
type of external oscillator is determined by FOSC2:FOSC0 as follows:
000 = LP1   low-power crystal (32 KHz)
001 = LP2   low-power crystal (32 KHz to 1 MHz)
010 = XT1   low-power crystal (32 KHz to 10 MHz)
011 = XT2   normal crystal (1 MHz to 24 MHz)
100 = HS   normal crystal (1 MHZ to 50 MHz)
101 = Reserved
110 = Reserved
111 = External RC
Note: The frequency ranges have not been characterized. These are target values.