[introduction] two-way bus line (for example, I 2 C, SMBus and LIN) already became in current electronic product nowhere is absent, partial reason depends on their simple sex. Use two lines only — data line and clock line — many equipment can correspond each other. According to standard of bus line of I 2 C, 128 many equipment can share same data and clock route; This is use through be on every equipment exterior on pull what resistance comes true with driver opening leakage. If do not have equipment to be in,transmit 0, criterion nature meets bus line be gone up to pull resistor to be pulled 1. But, any equipment on bus line can pull his for 0.

Two-way bus line introduces

Two-way bus line (for example, I 2 C, SMBus and LIN) already became in current electronic product nowhere is absent, partial reason depends on their simple sex. Use two lines only — data line and clock line — many equipment can correspond each other. According to standard of bus line of I 2 C, 128 many equipment can share same data and clock route; This is use through be on every equipment exterior on pull what resistance comes true with driver opening leakage. If do not have equipment to be in,transmit 0, criterion nature meets bus line be gone up to pull resistor to be pulled 1. But, any equipment on bus line can pull his for 0.

Allow bus line Master at any time drive bus line, slave answers the inquiry of bus line Master inside proper time

After receiving inquiry. In setting of much lead plane, the bus line that each equipment of lead plane of appropriative bus line need to carry out his is arbitral. The hope says or state with certainty to need to come through pulling its to the lead plane of pilot bus line of bus line 0 will have a test to its; This meeting announcement is other advocate equipment is using bus line.

Why fractionation two-way bus line?

Standard of bus line of I 2 C [1] includes a referenced circuit, allow to divide its be opposite for input and output. Stem from a variety of reasons to need this configuration. Above all, below the circumstance of safe, noise and ground connection problem, detached bus line can be used at lead plane of optical segregation bus line to mix from machine (graph 1) . In addition, can pass enlarge depart bus line (graph 2) or the circuit that changes with executive media replaces amplifier to realize function promotion. This can add the working space of bus line, improve performance through reducing electric capacity. Drop as capacitance, signal time is invariable T general by on play resistor decision.

 
Graph segregation of 1 two-way bus line

 
Graph 2 Repeater of two-way bus line

Design the person of controller of two-way bus line to those, can use technology of bus line fractionation to undertake debugging. The model of two-way agreement is debugged become difficult, because of the controller of misconduct the likelihood draws bus line 0, and another controller is saying or state with certainty the control to bus line. This kind of circumstance makes in do not know every device control character implement the transmission equipment that bus line cannot identify to go up below the circumstance of internal state of affairs. However, pursue through monitoring 2 medium / GateB1 and / GateA2 circuitry, can use standard lab only equipment and debug a technology to identify transmission equipment and bus line any say or state with certainty at the same time.

Technology of bus line fractionation can be used at joining the equipment that supports I 2 C another does not have the equipment of controller of I 2 C. Below this kind of circumstance, the GPIO that detached bus line can receive other equipment repeatedly (graph 3) .

Graph 3 Receive the fractionation bus line of GPIO repeatedly

It have a few circuit that already released is OK to have a few circuits that already released fractionation two-way bus line. Unfortunate is, the circuit that needs to be designed technically to specific applying with the referenced circuit or that applies at detached bus line (be like See at the article that already published) , or the exterior control that needs to use transmission door is logistic (if the place in I 2C standard is shown) allow transmitter and receiver to have communication, and won’t establish the feedback method that brings about latch. Latch circumstance is in graph 2 in apparently, among them IOA draws bus line to 0 force IOB to pass / GateB1 is pulled to 0, enforce next IOA is passed / GateA2 is pulled till the cows come home to 0.

The bilateral arbitration that in designing a concept originally, introduces implement can be fractionation of two-way bus line send and receive right, build with general pattern compose, make its can be used at application of any fractionation bus line. In addition, it does not need exterior control logic — bus line controls by the condition of data bus line only:

Graph 4 Bilateral arbitration implement make can circuit

Bilateral and arbitral

Graph 5 in shows arbitration implement by the graph 4 medium across coupling are made can circuit composition, act well, because the basis is defined,be, two-way bus line supports communication of half duplex operation only. Below steady state, DATA bus line be gone up to pull resistor R1 and R2 tall, force OUT1 and OUT2 for 0. This makes two NMOS FET are in off-state. When IC1 pulls low DATA, OUT1 turns into 1, make Q2 draws the DATA bus line of low IC2. In the meantime, OUT1 is gone to by feed or the input of blame door U2 is carried, disconnect to return the feedback loop of Q1 from OUT2. Of feedback loop this kind breaks pass the time in a leisurely way besides closedown condition, make any other control logistic become needless, because say or state with certainty the circuit of its data line won the contest, be passed or be not door block another circuit.

Graph 5 The bilateral arbitration of two-way bus line

 
Graph 6 bilateral arbitration enable bus line enlarge

As a result of the versatility of circuit, bilateral and arbitral applicable applies at any fractionation bus line. Graph 6 showed the bilateral arbitration that applies at enlarge. Replace amplifier package through using media change-over circuit or smooth isolator respectively, this can expand media changeover and bus line are kept apart easily. Stem from the purpose that debugs bus line controller, can the circuitry between monitoring amplifier identifies controller of fault bus line with the help. Graph 7 showed application arrives at I 2 C GPIO connective is bilateral and arbitral.

Graph 7 I 2 C joins to GPIO

Conclusion

two-way bus line cent is become send / receive to having a variety of reasons. From raise function to arrive enable debug arrive again segregation, bus line depart is a lot of a kind of design personnel ever discovered useful technology.

Bilateral arbitration is a kind of bus line arbitral technology, can realize application of fractionation of most bus line. It relies on the behavior that two-way bus line corresponds to eliminate the requirement of pair of exterior control circuit, and enough and general won’t increase needless complexity with be being used at a lot of application processes.

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