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SX20AC/SX28AC
5.0 DEVICE CONFIGURATION REGISTERS
The SX device has three registers (FUSE, FUSEX,
DEVICE) that control functions such as operating the
device in Turbo mode, extended (8-level deep) stack
operation, and speed selection for the internal RC oscilla-
tor. These registers are not programmable "on the fly"
during normal device operation. Instead, the FUSE and
FUSEX registers can only be accessed when the SX
device is being programmed. The DEVICE register is a
read-only, hard-wired register, programmed during the
manufacturing process.
5.1 FUSE Word (Read/Program at FFFh in main memory map)
TURBO
SYNC
Reserved Reserved
IRC
DIV1/
IFBD
DIV0/
FOSC2 Reserved
CP
WDTE
FOSC1
FOSC0
Bit 11
Bit 7
Bit 3
Bit 0
TURBO
Turbo mode enable:
0 =
turbo (instruction clock = osc/1)
1 =
instr clock = osc/4
SYNC
Synchronous input enable (for turbo mode): This bit synchronizes the signal presented at the
input pin to the internal clock through two internal flip-flops.
0 =
enabled
1 =
disabled
IRC
Internal RC oscillator enable:
0 =
enabled - OSC1 pulled low by weak pullup, OSC2 pulled high by weak pullup
1 =
disabled - OSC1 and OSC2 behave according to FOSC2: FOSC0
DIV1: DIV0
Internal RC oscillator divider:
00b
=
4 MHz
01b
=
1 MHz
10
=
128 KHz
11b
=
32 KHz
IFBD
Internal crystal/resonator oscillator feedback resistor between OSC1 and OSC2 pins (1 M
).
Disable if using an external clock:
0=
disabled
Internal feedback resistor disable (external feedback required
for crystal or resonator)
1=
enabled
Internal feedback resistor enabled (valid when IRC = 1)
CP
Code protect enable:
0 =
enabled (FUSE, code, and ID memories read back as scrambled data)
1 =
disabled (FUSE, code, and ID memories can be read normally)
WDTE
Watchdog timer enable:
0 =
disabled
1 =
enabled
FOSC2: FOSC0 External oscillator configuration (valid when IRC = 1):
000b = LP1 low power crystal (32KHz)
001b = LP2 low power crystal/resonator (32 KHz to 1 MHz)
010b = XT1 normal crystal/resonator (32 KHz to 10 MHz)
011b = XT2 normal crystal/resonator (1MHz to 24 MHz)
100b = HS1 high speed crystal/resonator/external clock (1MHz to 50 MHz)
101b = HS2 high speed crystal/resonator/external clock (1 MHz to 50 MHz)
110b = HS3 high speed external clock (1 MHz to 75 MHz)
111b = RC network - OSC2 is pulled high with a weak pullup (no CLKOUT output)
Note:
The frequencies are target values.