SX28ACSLASHSS datasheet(15/51 Pages) PARALLAX

15 / 51 page

Parallax SX20AC/SX28AC

www.parallax.com

Page 15 of 51

Rev 1.6 11/20/2006

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

oscillator. 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

IRC

DIV1/

IFBD

DIV0/

FOSC2

Reserved

WDTE

FOSC1

FOSC0

Bit 11

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 (1 MΩ:

0 = disabled

Internal feedback resistor disable (external feedback required)

1= enabled

Internal feedback resistor enabled (valid when IRC = 1)

Code protect enable:

0 = enabled (FUSE, code, and ID memories read back as garbled 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 crystal oscillator (1MHz to 50 MHz)

101b = HS2 - high speed crystal/resonator/external crystal oscillator (1 MHz to 50 MHz)

110b = HS3 - high speed crystal/resonator/external crystal oscillator (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.

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