RS-485 Txheej txheem cej luam
Zoo li RS-232, RS-485 yog tus qauv sib txuas lus sib txuas. Nws txoj kev xaiv tam sim no yog TIA-485 / EIA-485-A, tab sis nws feem ntau hu ua RS-485 tus qauv. RS-485 yog siv dav hauv kev lag luam xws li kev lag luam automation, tsheb, thiab kev tswj vaj tsev.
RS-485 tsheb npav kov yeej qhov tsis txaus ntawm RS-232, xws li kev sib txuas lus luv luv thiab cov ntaub ntawv tsawg. RS-485 txhawb cov ntaub ntawv tus nqi txog li 10 Mbit / s thiab muaj kev sib txuas lus theoretical txog li 1,200 meters. Tsis zoo li kev sib kis ib leeg ntawm RS-232, RS-485 siv qhov sib txawv ntawm kev sib kis ntawm ib khub ntawm cov xov hlau sib tw, nrog rau ib lub xaim raws li A thiab lwm yam li B.
RS-485 Lub cev txheej
Lub RS-485 lub cev txheej yog lub luag haujlwm rau kev xa cov ntaub ntawv nyoos ntawm cov khoom siv thiab lub cev sib kis nruab nrab. Nws tswj cov kev hloov pauv ntawm cov teeb liab hluav taws xob rau cov ntaub ntawv digital, thaum tseem txhais cov qib voltage, lub sijhawm, cov ntaub ntawv tus nqi, thiab lwm yam tsis.
① Cov teeb liab sib txawv
Ntev -kab kab nyob deb ua rau lub teeb liab attenuation thiab ua rau kom muaj suab nrov thiab cuam tshuam. Qhov no tshwm sim raws li kev hloov pauv ntawm qhov hluav taws xob amplitude ntawm cables A thiab B. Txawm li cas los xij, qhov zoo ntawm kev siv cov kab sib txawv yog tias rho tawm qhov sib txawv ntawm ob lub teeb liab tshem tawm qhov cuam tshuam, tso cai rau lub teeb liab ib txwm tso tawm. Lub peev xwm ntawm tus neeg txais kev sib txawv kom tsis quav ntsej qhov sib npaug ntawm ob lub teeb liab kab yog hu ua ntau- hom kev tsis lees paub.
Tus qauv qhia tias logic 1 yog +2V rau +6V, thiab logic 0 yog -6V rau -2V.
RS-485 tsis xav tau ib lub tsheb npav tshwj xeeb; nws tsuas yog txiav txim siab qhov tsawg kawg nkaus qhov sib txawv voltage. Tshaj qhov ntev cable ntev, qhov hluav taws xob tau txais los ntawm tus txais yuav poob mus rau +/- 200 mV, uas tseem zoo kawg nkaus rau RS-485-qhov no yog ib qho zoo ntawm RS-485.
Ntau lub transceivers tau ntsib lossis tseem dhau TIA / EIA-485A tus qauv; Txawm li cas los xij, hauv cov ntawv thov siv tau, txawm li cas los xij, cov cuab yeej tau teev tseg ua ntej. Piv txwv li, qhov tsawg kawg nkaus tsis zoo cov tswv yim pib rau ib qho transceiver yog -200 mV.
② Cov lus txhais
Ntau RS-485 converters niaj hnub no tau sib xws nrog RS-422, yog li koj feem ntau yuav pom cov cim npe T / R + thiab T / R- ntawm cov converters, uas sib haum rau RS-485's A + thiab B-.
Rau DB9 poj niam connectors, RS-485 thaiv cov lus txhais yog raws li nram no: Pins 6 txog 9 yog N / A thiab yuav tsum tsis txhob txuas.
| DB 9 | Tso zis teeb liab | RS -422 Full-Duplex Wiring | RS-485 Ib Nrab-Duplex Wiring |
| 1 | T/R+ | Xa (A+) | RS-485 (A +) |
| 2 | T/R- | Xa (B-) | RS -485(B-) |
| 3 | RXD+ | Txais (A+) | Npua |
| 4 | RXD- | Txais (B-) | Npua |
| 5 | GND | Hauv av Hlau | Hauv av Hlau |
③ Topology
RS-485 txhawb nqa ob-hlau thiab plaub-hloov teeb tsa. Plaub -hloov teeb tsa yog txwv rau taw tes- rau- taw tes kev sib txuas lus thiab tsis tshua siv niaj hnub no; ob-xaim configuration yog feem ntau ua hauj lwm. Qhov kev teeb tsa no siv lub tsheb npav topology, tso cai rau 32 qhov txuas rau ntawm ib lub tsheb npav.
Zoo li I²C, RS-485 tsheb npav ua haujlwm hauv tus tswv- hom qhev. Nws txhawb ob qho tib si taw tes-rau- taw tes ib leeg- qhev hom thiab ntau- qhev hom, tab sis tsis txhawb ntau hom tswv.
RS-485 Transceiver
RS-485 siv kev sib kis sib txawv. Yog tias koj xav tswj cov khoom siv RS-485 siv lub microcontroller, koj yuav xav tau lub transceiver-zoo ib yam li lub npav CAN. Daim duab hauv qab no qhia txog MCU tswj lub cuab yeej RS-485.
Nyob rau hauv lub transceiver yog ib tug receiver (saum ib nrab) thiab ib tug transmitter (qis ib nrab). Hauv qab no yog cov lus piav qhia luv luv ntawm yuav ua li cas lub transceiver ua haujlwm los pab koj nkag siab li cas MCU sib txuas lus nrog 485 ntaus ntawv.
Internal Structure ntawm RS-485 Transceiver
Qhov twg:
A thiab B yog lub tsheb npav;
R yog lub receiver input;
RE yog lub receiver pab teeb liab;
DE yog lub transmitter pab teeb liab;
D yog lub transmitter tso zis;
Rau cov cim qhia, cov uas muaj kab saum toj saud yog active - qis (piv txwv li, RE hauv daim duab saum toj no), thaum cov uas tsis muaj kab yog nquag siv - siab (xws li, DE).
Txais Qhov Tseeb Table
Rau lub transmitter, cov lus tseeb yog raws li nram no:
1. Thaum tus neeg tsav tsheb pab tus pin DE nyob rau ntawm lub logic siab, qhov sib txawv tawm A thiab B ua raws li lub xeev logic ntawm cov ntaub ntawv nkag D. A logic siab ntawm D ua rau A mus siab thiab B mus qis. Nyob rau hauv cov ntaub ntawv no, qhov sib txawv tso zis voltage, txhais raws li VOD=VA - VB, yog zoo. Thaum D yog qis, cov zis qhia invert: B mus siab thiab A mus qis, thiab VOD yog qhov tsis zoo.
2. Thaum DE qis, ob qho tib si tso tawm tau siab -impedance. Hauv qhov no, lub xeev logic ntawm D tsis cuam tshuam.
Cov lus tseeb hauv qab no siv rau tus txais:
1. Thaum lub receiver's enable pin (RE) nyob rau hauv lub logic qis, lub receiver yog qhib. Thaum qhov sib txawv input voltage, txhais raws li VID=VA - VB, yog qhov zoo thiab tshaj qhov zoo ntawm qhov pib VIT +, tus txais qhov tso zis R mus siab. Thaum VID yog qhov tsis zoo thiab qis dua qhov kev nkag siab tsis zoo VIT-, tus txais cov zis R mus qis. Yog tias VID nyob nruab nrab ntawm VIT + thiab VIT-, cov zis tsis tau txhais.
2. Thaum RE yog logic siab lossis ntab, cov khoom tso tawm tau siab impedance, tsis hais qhov loj lossis qhov polarity ntawm VID.
RS-485 Cov ntaub ntawv txuas
Tau tham txog cov qauv kev khiav hauj lwm ntawm RS-485 transceiver saum toj no, tam sim no peb yuav piav qhia luv luv ntawm RS-485 cov ntaub ntawv txuas. Tej zaum koj yuav xub saib seb qhov yooj yim to taub UART raws tu qauv qauv.
Txawm hais tias tus tswv xa cov ntaub ntawv mus rau tus qhev lossis tus qhev xa cov ntaub ntawv mus rau tus tswv, ob txoj kab A thiab B yog siv; yog li ntawd, RS-485 feem ntau yog siv nyob rau hauv ib nrab-duplex hom.
Tus tswv tsev GPIO tswj tus DE tus pin ntawm RS-485 transceiver los teeb tsa hom kis. Ib byte ib zaug xa los ntawm UART TXD kab mus rau cov ntaub ntawv (D lossis DI) kab ntawm RS-485 transceiver. Lub transceiver hloov pauv ib qho kawg UART me ntsis ntws mus rau hauv qhov sib txawv me ntsis ntawm kab A thiab B. Thaum cov ntaub ntawv tawm ntawm lub transceiver, tus tswv tsev tam sim ntawd hloov lub transceiver kom tau txais hom.
Tus qhev ua haujlwm zoo ib yam li tus tswv. Tus qhev tswj tus /RE tus pin ntawm RS-485 transceiver los teeb nws kom tau txais hom, tau txais cov kwj me ntsis xa los ntawm tus tswv, hloov nws mus rau ib qho teeb liab-kawg, thiab tau txais los ntawm tus qhev txoj kab UART RXD. Thaum tus qhev npaj txhij los teb, nws xa cov ntaub ntawv tib yam li tus tswv, thaum tus tswv hloov mus txais hom.
Hloov ua lwm yam RS-232 rau RS-485
Nws tuaj yeem hloov pauv ntawm RS-232 thiab RS-485. Ib txoj hauv kev yog hloov RS-232 rau TTL, thiab tom qab ntawd hloov TTL rau RS-485. Tau kawg, kuj tseem muaj cov chips uas txhawb kev hloov pauv ncaj qha los ntawm RS-232 rau RS-485, thiab ntau cov qauv no muaj nyob hauv online.
RS-232 rau RS-485 Hloov Modules
Qhov txawv ntawm RS-485 thiab CAN
Txawm hais tias RS-485 tsis muaj cov qauv ntaub ntawv raws tu qauv, nws muaj ntau qhov sib xws nrog lub npav CAN. Piv txwv li, ob qho tib si A&B thiab CANH&CANL yog cov cim sib txawv; ob leeg xav tau transceivers rau kev sib txuas lus; thiab ob leeg siv 120-ohm termination resistors, ntawm lwm yam zoo sib xws.
| Cov yam ntxwv tsheb npav | CAN Bus | RS-485 UAS |
| Cov nqi kho vajtse | Siab dua me ntsis | pheej yig |
| Kev siv tsheb npav | Tsis siv neeg qhov tseem ceeb arbitration, siab siv | Siv kev xaiv tsa; kev siv tsawg |
| Cov Ntaub Ntawv Hloov Tus Nqi | Siab | Tsawg |
| Yuam kev Detection Mechanisms | Tus maub los suav nrog lub tshuab kuaj xyuas kom ntseeg tau qhov tseeb ntawm cov ntaub ntawv qis- theem | Tsuas yog cov txheej txheem ntawm lub cev; tsis muaj cov ntaub ntawv txuas txheej txheej specifications |
| Kev cuam tshuam ntawm ib leeg -Node Failure | Tsis muaj kev cuam tshuam rau lub npav | Bus paralysis |
| Tus nqi tsim kho | Kev txhim kho software yooj yim, siv sijhawm tsawg | Yooj yim rau kev txhim kho |
| Cov Nqi Them Nqi | Tsawg heev | Siab |
Common RS-485 Circuit Court
Nov yog ib qho RS-485 Circuit Court uas kuv pom hauv online. Muaj ob lub ntsiab lus kom nco ntsoov:
1. Cov cim qhia RE thiab DE tuaj yeem tswj tau los ntawm ib qho GPIO kom txuag tau cov peev txheej. Thaum GPIO25 tso tawm ib theem siab, RE thiab DE yog 0 V, thiab cov cuab yeej nkag mus tau txais hom; thaum GPIO25 tso tawm ib theem qis, RE thiab DE yog 3.3 V, thiab cov cuab yeej nkag mus rau hom kis.
2. Hauv qee lub voj voog, rub-nce resistor ntxiv rau tus pin A thiab rub-down resistor rau tus pin B. Qhov laj thawj tseem ceeb ntawm qhov no yog vim li cas, thaum lub tsheb npav RS -485 nyob rau hauv lub xeev tsis ua haujlwm, qib voltage tsis ruaj khov- uas yog, nws fluctuates ntawm -200 mV los yog siab transverse {{200} mce thiab V. qib qis. UART yuav tsum tswj hwm qib siab thaum tsis ua haujlwm; Yog tias lub transceiver tso tawm qis qis rau lub sijhawm no, UART txhais tau tias nws pib me ntsis, uas tuaj yeem ua rau kev sib txuas lus yuam kev. Qhov tshwj xeeb qhov tseem ceeb ntawm R_u thiab R_d yuav tsis tham txog qhov no; Kuv npaj yuav sau ib tsab xov xwm ntxaws txog lub ncauj lus no yav tom ntej.
Hais txog lub ntsiab lus thib ob, thov nco ntsoov cov hauv qab no:
① Yog tias koj siv lub rub-nce resistor rau tus pin A thiab rub-down resistor rau tus pin B, cov ntaub ntawv kev sib txuas lus yuav ua tsis tau vim yog kev sib txuas rov qab.
② Yog tias lub transceiver tau tsim -hauv rub- nce thiab rub- cov resistors, tsis tas yuav ntxiv cov khoom sab nraud.