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Another set of backplane architectures that is finding a level of interest is the mesh backplane. Since there is no switch, the complexity of handling these multiple point-to-point signals now resides on the function card. Something needs to be available on either the transmitting or receiving function card that identifies the data. On the transmitting function card, the data would need to be directed to the receiving function card that requires the data. Or, if the transmitting function card does not discriminate, then the receiving function card must identify the data that it requires.

ERJ-P03D10R0V_Datasheet PDF

Another set of backplane architectures that is finding a level of interest is the mesh backplane. Since there is no switch, the complexity of handling these multiple point-to-point signals now resides on the function card. Something needs to be available on either the transmitting or receiving function card that identifies the data. On the transmitting function card, the data would need to be directed to the receiving function card that requires the data. Or, if the transmitting function card does not discriminate, then the receiving function card must identify the data that it requires.

Once an appropriate standard has been selected, the bus design can be optimized for reliable transmission of data at high rates. Note that each wireline standard may have different ranges of operation, so that the actual signaling rates considered high” may vary from standard to standard. The following discussion will in general apply across a wide range of standards, with some tailoring to any specific application.

Error rate: The fundamental limitation on increasing the signaling rate across any bus is the requirement to maintain a low rate of errors in the transmitted data. For wireline data transmission, the major sources of error are:

ERJ-P03D10R0V_Datasheet PDF

signal attenuation due to cable effectssignal reflections caused by improper terminationinduced voltages coupled from electrical noise sourcessynchronization faults due to finite signal transition time and transmission delays

Electrical noise (crosstalk, EMI, etc.): As signaling rate is increased, the effects of electrical noise, especially at high frequencies, become more of a concern. All cables, printed etch, and even component leads tend to act as antennas, both receiving and radiating electrical energy. The dominant wavelength of the antenna is inversely proportional to the fundamental frequency. Therefore, as the fundamental frequency is increased, even relatively short line lengths become efficient antennas for radiating and receiving electrical noise. The noise coupling (both the magnetic field coupling and electrical field coupling) reaches an effective maximum when the wavelength is four times the line length. The table below relates this condition (quarter wave antenna) to the fundamental frequency of the data bus.

In order to reduce the electrical noise generated by the data transmitter, the fundamental frequency should not exceed what is strictly required by the application. This means that the rate of signal transition (slew rate) should be controlled to reduce emitted noise. Similarly, to reduce the received electrical noise on a data bus, the frequency response of the receiver should be limited to only the frequency range of the valid data.

ERJ-P03D10R0V_Datasheet PDF

Power consumption: The power dissipation of any wireline bus system has both dc and ac components. As the signaling rate increases, the ac power dissipation also increases. The following figure illustrates the increase in supply current at the bus driver for three different bus standards. In all cases, higher data rates incur a cost of supply current; the LVDS curve illustrates the advantage of lower signaling levels and a controlled current-drive circuit.

ERJ-P03D10R0V_Datasheet PDF

Termination Effects

FR architecture

The RISC possesses a 5-level pipeline (read, decode, execute,memory access, write). The architecture requires a Harvard busstructure (separate bus for data and programs) to guarantee theeffective execution of the program. This ensures that commands can beprocessed even within an instruction cycle.

The characteristics of a pipeline structure are in a sense highlycomplex, as the correct sequential processing of the software must beguaranteed (e.g. writing register content at the same time as theregister in question is being reprocessed, etc.).

However, in general, conditional jump instructions should only beprocessed by adding an 'NOP' instruction. By way of contrast, the FRhas special commands for the latter, such as the delayed branch, forexample. This ensures that the code is processed without executingNOPs.

Other FR core characteristics include the 16 universal registers,separate stacks for user and system programs, a bit search functionalblock, a 32bit x 32bit multiplication block and the 16bit instructionset.

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