Interfacing X9408/X9418 XDCP 8051 Microcontrollers This applicati

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Interfacing X9408/X9418 XDCP 8051 Microcontrollers This applicati

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AN114
Interfacing X9408/X9418 XDCP 8051 Microcontrollers
This application note describes routines control X9408 X9418 digitally controllable potentiometer. X9408/X9418 devices have variety different instructions that provide flexibility designer. Additionally, nonvolatile nature device allows stored wiper positions that retrieved after power cycles. following code implements available X9408/ X9418 instructions using standard bi-directional protocol. Although routines occupy less than bytes program memory, designers won't need implement instructions shorten code removing unnecessary routines. However, this will necessitate reassembly code. those instructions which program nonvolatile data registers (XFR_WCR, GXFR_WCR, WRITE_DR), acknowledge polling been implemented determine early completion internal write cycle. Although this automatically handled routines, word regarding procedure should informative. After issuing start condition, master sends slave address receives acknowledge. then issues instruction byte X9408/X9418 again receives acknowledge. necessary, transmits data byte receives final acknowledge. master must then initiate stop condition which will cause X9408/ X9418 begin internal write cycle. X9408/X9418 pins high impedance until this internal cycle complete. master begin acknowledge polling successively sending start conditions followed "dummy" instructions. When X9408/X9418 finally answers with acknowledge, internal write cycle been completed. master must then initiate stop condition. After next start condition, X9408/X9418 ready receive further instructions.
P0.0 P0.1 P0.2 P0.3 P0.4 P0.5 P0.6 P0.7 P2.0 P2.1 P2.2 P2.3 P2.4 P2.5 P2.6 P2.7 PSEN ALE/P 80C51
EA/VP
RESET INT0 INT1 P1.0 P1.1 P1.2 P1.3 P1.4 P1.5 P1.6 P1.7
X9408
Figure Connecting X9408 80C51 microcontroller
AN114-1
Xicor code listing, assumption made that code executes upon reset microcontroller. That code loaded into memory, however this changed with assembler directive. simple MAIN program exercise these routines included code listing. this listing, commands cause X9408/X9418 A3A2A1A0 0000) accessed EEPOT rewritten with value (for wiper position #43). Then pulse decrement wiper initiated, causing selected reduced value (for wiper position #28).
AN114
issuing other commands follows same general procedure. Figure representative hardware connection between X9408 8051 family microcontroller shown. pull-up resistors lines determined total capacitance devices connected bus, which about 18pF. this case, however these necessary since port pins 8051 family devices have internal pull-ups.
AN114-2

Interfacing X9408/X9418 XDCP 8051 Microcontrollers This applicati

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