application n o te AN2352 i2c-usb bridge usage author : valeriy kyrynyuk asso ciated project : yes asso ciated part family : cy8c248 94 soft w a re version : psoc de sign er? v . 4.3 asso ciated applica t ion notes and kits : an23 04, cy324 0-i2 usb, cy3242-i o x >> availa ble in cypress onlin e store abstract t h is applicati o n note, w h ich is inclu d e d in the cy32 40-i 2 u sb kit ava i l abl e in the c y press onli ne store, detai ls severa l examp l es usin g the i2c-usb brid ge d e sig n . it is a l so a s u ppl ement t o th e i2c-usb bridge quick st art guide reference [2] at the end of this docum ent, als o avail a b l e in cy32 40-i2us b. t h e appl ica t ion note co ntains d e tails a b out implem enti ng an i 2 c interface i n to e x isti ng pr ojects and usi ng i 2 c communic a tio n to test, debug and tun e dev ic e desi gns. introducti on t he normal capa bil i ties of a pc can be w e ll e x pa nde d upo n b y usi ng the ne w i2c- u sb bridg e an d its supporti ng soft w a r e . a p c w i th i2c- u sb bri dge ca n be usef ul for follo w i ng tasks: ? deb ug e x isti ng projects (usi ng i 2 c communic a tion instea d of uar t , for exampl e) . ? acquir e an d mani pul ate data from various i 2 c devic es, such as adcs, dac s , io exp and er s, sensors w i t h i 2 c interfaces, et c. ? program eep rom, sram devices. ? t r ain users an d demo n strate i 2 c devic e cap abil i ties. t h is applicati o n note d e tai l s the follo w i n g exampl es of brid ge usa ge: 1. monitori ng c a p s ense cs r us er modu le o per ation. 2. monitori ng tac hometer o per ation. 3. w o rking w i th a 20- pi n io port e x p a nder w i th eeprom. 4. programming 24cxxx ser i al eeprom devices. 5. w o rking w i t h a psoc-bas ed 3 - chan nel p o ten t iometer. t he simplest w a y to im plem ent i 2 c into a psoc proj ect and attach the dev ice to the brid ge w i l l a l so be lo oke d at closel y. t h is docum ent do e s not descri b e the inter nal structure a n d protoco l of the bri dge. f o r th is i n formatio n refer to the i2c-usb bridge guide refere nce [1] at the end of this doc um ent, also avai l abl e in c y 32 4 0 -i2usb. t h e usb2iic.exe p r ogram w a s us ed in al l e x amp l es. details o f this progr am ar e descri bed i n [2]. attach device t o br idge exec ute the fo llo w i n g steps to conn ect the devic e to the i2c-usb bridge: 1. con nect gnd of the devic e to gnd of the bridge. 2. con nect the sda, scl lines to the bridg e (f igure 1). bridg e has 2.2 k pull- up resist ors conn ected to + 5 v. 3. po w e r th e dev i c e from the vd d pin on th e br idg e if it does not h a ve its o w n po w e r supp l y . note that the conn ectio n of vdd bet w e en the bridg e a nd targe t boar d is re quired, eve n if th e b oar d is s e lf- po w e red. t he bridg e can (o ption a ll y) pr ovi de 3.3v o r 5v, or it can w o rk w i th a n ext e rna l l y po wered b oar d usin g 2.4v to 5 . 6v. 4. con nect the bri dge to usb. 5. run usb2iic.exe program from pc. 6. select the bri d ge i n the l i st at the bottom c e nter of the screen. 9/22/2006 revision ** - 1 -
AN2352 7. click th e lis t button in the usb2iic.exe program. t he list of a ll c onn ected i 2 c d e vices w i l l app ear. not e that if the bri d g e is pr ovid i ng po w e r, it is nec essar y t o turn the po w e r on befor e the lis t button w i ll w o rk. no w d e sig ners can w o rk w i th all liste d dev ice s . figure 1. i2c-usb bridge implement i 2 c inter f ace i n to psoc a tool that can contin uous l y collect an d di spla y vari ab le valu es is v e r y useful d u rin g de bu ggi ng/t e sting psoc- base d pro j ects . readi ng me a s ureme n t resul t s, pin states and d y n a mic modific a tion of devic e pr op erties are tasks commonl y p e r f ormed b y d e sig ners. t h e uart user module is frequently used for such tasks. but such a method co ntai ns severa l disa dvanta ges: ? t he design r e q u ires o ne s par e dig i tal ps oc block for half-d upl e x u a rt operatio n. (t he i 2 c i n te rfa c e hard w a r e is i n d epe nd ent of the dig i tal bl ocks .) ? some com pute r s, particul a rl y noteb ooks, d o not hav e com ports a nd c o mmun i c a tion ca pab iliti e s for a uart . a usb-uart bridge is need ed. ? t he add ition a l lev e l-br idg e , such as a m ax232, is necess a r y on the des ig ned b oard. ? t he band w i dth of an i 2 c-us b brid ge is gr e a ter tha n the ban d w i d th of a standard uart . t he maxim u m ban d w i d th for a uart is about 11 kb/s, but i2c-usb brid ge can attain a 25kb/s b a n d w i d th. t a king into acc ount ev er y t hin g menti one d a bove, us ing an i2c-usb br id g e is m o re s u it abl e a nd c h e a per th an other solutions. t o implement the i 2 c slave i n terface into a psoc pro j ect, the follo w i n g steps are re qu ire d : ? place the ezi2 cs user mod u l e in the pso c proj ect. ? set the follo w i ng user module parameters: o slave _ ad dr to 1 (this addr e ss can be almost an yth i n g , it is not restricted to 1) o address _ t y pe to static o rom_register s, in most cases, to disab le o i 2 c clock to 400 khz fast o i 2 c pins to p1[ 0 ]-p1 [1] or p1[5]-p1[7] ? defin e the ra m buffer that w ill cont ain d a ta requ ired for i 2 c transmi ssion. defi ne the arra y or stru cture w h os e ad dress w i ll be s pecifi e d w h e n the setram buffer function is ca ll ed . f o r exampl e: struct i2c_regs { // example i2c interface structure word wx1; // read/write value int iadc; // read only value byte bstatus; // read only value } myi2c_regs; ? insert, into the initia liz at ion p a rt of program, the follo w i n g t w o st rings: ezi2cs_setrambuffer(ci2cread,ci2cwrite,(byte *)&myi2c_regs); ezi2cs_start(); ? set the argum ents of e z i2cs _setra mb uffer function to proper va lu e s . length of da ta, w h ich cou l d be read, is set by ci2cread argum ent and le ngth of data, w h ich c oul d be w r itten, is set b y ci2cwrite . t he addr ess of the i 2 c buffer is set b y myi2c_regs, wh i c h is the third arg u ment. once the ab ov e steps are c o mplete, ther e i s no ad ditio n a l code req u ire d to sup port i 2 c communic a tio n . t he ezi2cs user mod u l e w o rks in th e b a ckgro und w i t h i 2 c interru pt han dlers. t he first by te receiv ed b y i 2 c slave is th e offset into the buffer from w here d a ta w i ll be rea d from or w r itten to. defau l t offset is 0. t here is on e as pect t hat sh oul d be consi dere d w h en w o rkin g w i t h the i 2 c buffer. if the size of the var i ab le go ing into the buf fer is gr eater than 1 b y t e , a speci a l tech ni q ue must b e us ed. f i rst, al w a ys d i sa ble th e interru pt befor e chan gi ng or readi ng this varia b le i n the progr am. sec ond, v e rif y th e p e rmissib ilit y of vari abl e access. t o implem ent this, t he pr ogram m u st ana l y ze th e ezi2cs bram _rw c ntr varia b le. t h is varia b le p o i n ts to current tra n smi ssion in de x of the i 2 c b u ffer. w i thout suc h ana l y sis, the si tuation d e p i ct e d in f i gur e 2 can occur. 9/22/2006 revision ** - 2 -
AN2352 f i g u r e 2. examp l e o f erro neo u s t r an smissio n o f w o r d -t y p e va riab le 00 ff 255 w o rd ty pe v a r i able into i 2 c buffer cur r ent buffer i ndex of i 2 c int e r r upt ser v i c e i 2 c sends 00 h t h is is msb by te of w o rd val u e 01 00 256 w o rd ty pe v a r i able into i 2 c buffer cur r ent buffer i ndex of i 2 c int e r r upt ser v i c e step 1. i 2 c sends m s b by te of w o rd valu e step 2. program upda tes i 2 c buffer w o rd v a lue chan ged by 1 01 00 256 w o rd ty pe v a r i able into i 2 c buffer cu r r ent buffer index of i 2 c inter r upt se rvi c e step 3. i 2 c s e nds ls b by te of word valu e i 2 c sends 00 h t h is is ls b by te of w o rd val u e 9/22/2006 revision ** - 3 -
AN2352 belo w is the si mple e x am pl e of i 2 c slave im plem entatio n in a psoc pr oj ect: cod e 1. i 2 c sl ave implem ent ation extern byte ezi2cs_bram_rwcntr; struct i2c_regs { // example i2c interface structure word wx1; //read/write value int iadc; // read only value byte bstatus; // read only value } myi2c_regs; void main() { word wlop; int ia; ezi2cs_setrambuffer(5, 2, (byte *) &myi2c_regs); // set up ram buffer m8c_enablegint; // turn on interrupts ezi2cs_start(); // turn on i2c ............ // wx1 access m8c_disablegint; //!!! turn off interrupt if variable holds more than 1 byte! if (ezi2cs_bram_rwcntr!=1)wlop=myi2c_regs.wx1; m8c_enablegint; // turn on interrupt ........... ............ // iadc access m8c_disablegint; //!!! turn off interrupt if variable holds more than 1 byte! if (ezi2cs_bram_rwcntr!=3) myi2c_regs.iadc=ia; m8c_enablegint; // turn on interrupt ........... ........... // bstatus access is not need interrupt disable myi2c_regs.bstatus=0x20; ........... } ex am ples of bridge usa g e d u ring te sting a nd de bugging proj ects as w a s d e scri bed earl i er, th e i2c-usb bri dge is an id eal appr oach t o a pc-bas ed d a t a acqu isitio n s y stem. t he collect ed d a ta can b e use d to cali brate, rate accur a c y , optimiz e devi c e param eter s and pre p a re rep o rts. hard w a re co nfi gurati on of suc h a s y stem i n cl udes a n i2c- usb brid ge, a pc w i t h w i nd o w s ? 20 00\ xp i n stall ed, an d a commu nica tion pr ogr am (in this d e sig n it w a s usb2iic.exe ). let?s cons ider ho w a pc-ba s ed data ac qu isition s y ste m can be used to test an d d ebu g pro j ects b y e x am ini n g three examp l es. t he first e x am p l e is a tach o m eter pro j ect (test2_t ach project). t h is proj ect measu r es the inp u t freque nc y (r an ge 20- 200 00 hz) and se nd s this value to the pc via the brid ge. t he inp u t frequenc y e n ters throug h port pi n p 0 [7] and t he i 2 c i n terface uses p 1 [5] an d p1[7]. t he slave_a d d r par ameter is 0. t he comma nd l i ne for the usb2iic.exe p r ogram, w h ich reads tach ome t er values, is as follo w s : s 01 xk3 xk2 xk1 xk0 p f i gure 3 sho w s a di agr am of d a ta c o l l e c ted from t h e tachometer. 9/22/2006 revision ** - 4 -
AN2352 f i g u r e 3. t ach o m eter me asu rem e n t s t he second e x am pl e pr oject (test3_ca p ) d e monstrates a caps ense- driv en ke yp ad. it indic a tes a n d collects dat a from the csr user mod u le measurem ent s. t h is data hel ps mo nitor ke ypa d perfor m ance a nd opt imize the csr user mod u le p r operti es an d pcb la yo ut. t he slav e_a ddr param eter for t h is e x ampl e is set to 5. f i gur e 4 sho w s the oper ation of this proj ect ? the perio d valu e duri n g sequ enti a l pres sing of ke yp ad buttons. t he command line of this exa m ple is as fol l o w s : s 0b xk1 xk0 xl1 xl0 xm1 xm0 xn1 xn0 p f i g u r e 4. csr ke y p ad perio d samp les k g f e d c b l g f e d c b m g f e d c b n g f e d c b 40 0 35 0 30 0 250 200 150 10 0 50 0 6 00 0 5 50 0 5 00 0 4 50 0 4 00 0 3 50 0 3 00 0 2 50 0 2 00 0 9/22/2006 revision ** - 5 -
AN2352 t he third exa m ple pr oject ( t est4_adc3) demo n strates a lo w - cost, thre e chan nel, l o w - f r equ enc y osc ill oscop e bas ed on the cy8c 2 7 x43 devic e a nd us es a pc . t h is proj ect can be mo difie d to a larger n u mber of cha n nels (u p to 8) and great er a dc reso luti on (up to 1 2 b i ts). t he current proj ect uses a t r iadc8, w h i c h can attai n p e rformanc e of up to 600 0 sa mples p e r sec ond for eac h chan nel. t he burst mode of the brid ge tr ansmits this d a ta to the pc. in burst mode, the bri d g e transmits u p to 25 kb/s, w h ic h is eno ugh ba nd w i dth for this proj ect. f u rthermore, thi s proj ect allo w s desi gners to c han ge the pga gain val ue. t he pga gai n ca n b e d y n a mical l y adj us ted for better sensitivit y, w h i c h all o w s me a s ureme n t of a w i der r a n ge of sign als. t he first three b y t e s i n the i 2 c buffers are the pga gai n val ues, w h ich hav e t he pga_s e t_gain functi on format. f o llo w i n g is th e comma nd li n e that sets up a ga in v a l ue fo r each an al og in put: first in put gai n is set to 2 (0 x7 8 va lue), secon d in put g a in is s e t to 1 (0xf 8) and th ir d inp u t gai n is set to 0.5 (0x 7 0). s 02 00 78 f8 70 p t o read adc samples, the offset addres s for the adc data into th e i 2 c buffer should be set first at: s 02 03 p t he follo w i ng comman d strin g w i l l re ad s a mples from th e devic e in hi gh- spee d burst mode: s 03 xk0 xl0 xm0 p t he samples w e re rec o rde d at about 1 0 seconds. a dia g ram of the receiv ed dat a i s sho w n b e l o w (f igure 5). figure 5 . thre e cha nne l a d c sa mple s 9/22/2006 revision ** - 6 -
AN2352 io expander usage w i th bridge a goo d e x am ple of i2c-us b brid ge im pl ementati on is usag e of the c y pr ess io port e x p and er, cy8 c 95 20 . comman d li ne exampl es us i ng usb2iic.exe , for w o rking w i t h the 20- pi n io expa nd er, are descri bed b e lo w . t he cy8c95 2 0 e x p a n der h a s 20 pi ns, w h ich can be separ atel y c o n f igure d to s e v e ral m o d e s. t he c o mman d string be lo w sh o w s ho w pins on io exp and e r port 0 can be config ured ( ta ble 1 ). register 0x18 selects w h ich expa nd er port i s to be config u r ed. s 42 18 00 s 42 19 9f 00 cd 71 04 02 10 80 01 48 20 ta ble 1 . pin confi gura t ion o f ex pa nde r port 1 regist er value descrip tion 19 9f interrup t mask register 1a 00 pwm output r e gister 1 b c d i n v e r s i o n r e g i s t e r 1 c 7 1 input/out p u t reg i s t e r 1d 04 pull up drive mode pins 1e 02 pull dow n drive mode pins 1f 10 open d r ain high drive mode pins 20 80 open d r ain lo w drive mode pins 21 01 strong d r ive mode pins 22 48 strong slo w d r ive mode pins 23 20 high z drive mo de pins t he state of exp a n der i n p u ts can b e re ad f r om regist ers w i t h 0..2 address: s 42 00 s 43 x x x p t he pins? outp u t data are c o ntro ll ed b y re gi sters that hav e 0x08..0 x0a ad dress. t he follo w i n g e x ampl e turns to zero all o u tputs of p o rt 0 and turn s to 1 all out puts of port 1: s 42 08 00 ff p t he interrupt status regist ers can be read to detect expa nd er in pu t activit y . t h is feature is v e r y us eful for counti ng qua nti t y of certa i n ph ysic al v a lu es s u ch as w a ter, gas or electric it y . t he interr upt status reg i sters start a t register 0 x 1 0 . belo w is a co mmand stri ng that rea d s th e interru pt status from all three expa nd er ports : s 42 10 s 43 x x x p rememb er th at the interr up t status reg i ster is up date d each tim e a n activit y on th e in put p i n is prese n t an d interrupt mask bit of the pin is set to 0 (register 0x19). t he cy8c9520 expand er also has sever a l pwm blocks, w h ich outp u t can be direct ed to the o u tput pins. t h e freque nc y ra n ge for th e p w ms is from 12 m h z to 0.000 00 01 hz. t h e y can b e u s ed for transforming a di gital sign al to a pu l s e-dur ation a n a lo g si gn al, or even as a l o w - spee d dac w i t h hi gh-res i s t ance o u tput. t he examp l e bel o w sh o w s the initi a liz ation strin g s, w h ich tur n the pw m1 to a fre que nc y of 3.5 hz w i t h 50% d u t y c y cle. t he output of the pw m is sent to pin 2 4 of the e x p a n der (port1[3]): s 42 18 01 s 42 1a 08 p //set pwm pin s 42 21 01 s 42 1a 08 p //set pin mode s 42 28 00 s 42 29 04 68 34 p //set pwm1 parameters moreov er, the cy8c9520 ex p ander has built -in eeprom, w h ich is av ail abl e for use w i t h i 2 c m a ster. t o ena bl e eeprom, use the follo w i ng string: s 42 2d 43 4d 53 02 p once this com m and stri ng e x ecutes, eepr om is avail a b l e at address 0 x 8 0 + e xp an der a ddress, or 0 x a 2 , in this case. let?s w r ite 8 b y tes to eeprom address of 0 x 0 0 2 0 : s a2 00 20 00 11 22 33 44 55 66 77 p no w , w e w i ll re ad 4 b y tes fro m address 0 x 0 024: sa2 00 24 s a3 x x x x p 9/22/2006 revision ** - 7 -
AN2352 t h e e x pa nd er a l l o w s desi g ne rs to sa ve cu rre n t config uratio n s e ttings to ee prom. in future us e, thes e config uratio n s e ttings can be automatica l l y load ed u pon start up. use the comm and string b e lo w t o save curre nt config uratio n s e ttings as d e fa ult: s 42 30 01 p f o r more detai l s on port e x p a nder o per ation, refer to [3]. progr am ming i 2 c eeprom usi ng bridge t he cy8c9 5 2 0 e x p a n der c a n be us ed to w r it e a nd r e a d data from sta n dard i 2 c eep rom or sra m devic es. t he progr am bintousb2iic.exe , w h ich w a s add ed to th is appl icatio n not e , conv erts b i n a r y d a ta to a c o mman d fil e . t o program the devic e, th e g e n e rated comman d fil e shou ld b e op ene d in usb2iic.exe pro g r am and a l l comman d strin g s e x ecut ed. t he follo w i ng steps must be performe d to program a n i 2 c memor y dev ice: 1 . d e te rmi ne the i 2 c a ddr ess of the devic e to b e progr ammed. t o do this, cli ck the scan bu tto n an d choos e the a ppro p riate a d d ress from the list of ide n tified devic es. 2. pass the bi nar y fil e (dat a for programm i ng) throug h the bintousb2iic.exe pro g ram. t h ree parameter s must be e n te red int o the comman d li ne of the progr am: file n a me of i n p u t and outp u t file s (defau lt output file is data.txt ) and de vice i 2 c addre ss (default is 0xa 0 ). f o r exam pl e: bintousb2iic.exe data.bin data.txt a2 3. open the o u tput file in the usb2iic.exe program. send a ll com m and strin g s b y ch eckin g the ?send all strings? bo x a n d clickin g the se nd button. after this, the device w i ll b e pr ogramm ed. concl u si on t h is applicati o n note dem on strates ho w t o effectivel y p a ir an i2c-usb bridg e w i t h the usb2iic.exe soft w a r e progr am. if interested, r ead throu gh th e doc umentati on o n the brid ge i n te rnal pr otocol a nd structure [1 ]. it is also an adva n tag e to be famil i ar w i t h w r itin g soft w a re that w o rks w i t h usb hid dev ices. t he source code of the usb2iic.exe progr am is a goo d starting poi nt for such desi gni ng. refer e nces [1]. i2c-usb bridg e guide , in clud ed in the c y 324 0-i2us b kit avail abl e in the c y press o n lin e store. [2]. i2c-usb bridge quick start guide , inclu ded i n the cy32 40-i2us b kit availa ble i n the c y press onlin e store. [3]. an230 4 ? i 2c port e x p and er w i t h f l ash stor age? http:// w w w . c y p r ess.com/desi g n/an23 04 as sociat ed pr oje c t and support material s name descrip tion test2. z i p tachometer e x a m ple project test3. z i p capsense ke yp ad example pr oject test4. z i p three channel a dc exam ple project usb2iic.exe pc soft w a re f o r i 2 c-usb bridge bittiusb2iic.e xe pc soft w a re f o r binar y dat a con v ersion about the author nam e : valeriy k y r y nyuk title : engi neer ba ck ground : eight years e x peri ence w i t h field bus a nd co mmunicati on devic e desi gns . conta c t : lopik @ lviv.farl e p .net cy pres s s e mi co n duc to r 198 c h am pio n c o urt s an j o s e , c a 951 34- 17 09 p h on e: 40 8-9 4 3 - 2 6 00 f a x : 408-9 4 3 - 4 7 3 0 htt p ://w ww .c y p res s .c om ? c y pr ess semi cond u c tor c o r por ati o n , 200 6 . t h e i n f o r m a ti o n cont ai ned h e r e i n i s subj ect to chang e w i thout not i c e. c y pr ess semi co nd u c to r co rp o r atio n a s su m e s n o re sp on sib ilit y f o r th e use o f any ci r c ui try other than ci r c ui tr y embod i ed i n a c y pr e ss pr oduct. n o r does i t conv ey or i m pl y any l i c ense under pat ent o r ot her r i g h ts. c y pr ess pr oducts ar e not w a r r a nted no r i n tende d to be us ed f o r m edi cal , l i f e sup por t, l i f e sav i ng , cr i t i c al contr o l or safe ty appl i c ati ons, u n l e ss pur s ua nt to a n ex pr ess w r i t t en ag r eeme n t w i t h c y pr ess. fur t her mor e , c y pr ess does not a u thor i z e i t s pr oducts for use a s cr i t i c al compo n e n ts i n l i f e- supp or t sy stems w her e a mal f u n cti o n or fai l u r e m a y r eason abl y be ex pected t o r e su lt in sign if ic a n t in jury to th e u s e r . t h e i n clu s io n of c y pr ess pr oducts i n l i f e- supp or t sy stems app l i c ati on i m pl i e s t hat the ma nu factur er assu me s al l r i sk o f suc h us e a n d i n doi ng so i n de m n i f i e s c y pr ess ag ai nst al l char g e s. 9/22/2006 revision ** - 8 -
|
