mipi dsi and d-phy reading notes
1. High speed mode of Start-of-Transmission (LP-11 ->LP-01 -> LP00 -> HS-0)
TX :TX-Side / RX: RX-Side
[TX] Drives Stop state (LP-11) ->
[RX] Observes Stop state
[TX] Drives HS-Rqst state (LP-01) for time TLPX ->
[RX] Observes transition from LP-11 to LP-01 on the Lines
[TX] Drives Bridge state (LP-00) for time THS-PREPARE ->
[RX] Observes transition form LP-01 to LP-00 on the Lines, enables Line Termination after time TD-TERMEN
[TX] Enables High-Speed driver and disables Low-Power drivers simultaneously ->
[TX] Drives HS-0 for a time THS-ZERO ->
[RX] Enables HS-RX and waits for timer THS-SETTLEto expire in order to neglect[nɪ'glekt](忽略,忽视) transition effects
[RX] Starts looking for Leader-Sequence
[TX] Inserts the HS Sync-Sequence ‘00011101’ beginning on a rising Clock edge ->
[RX] Synchronizes upon recognition of Leader Sequence ‘011101’
[TX] Continues to Transmit High-Speed payload data
[RX] Receives payload data
2. High speed mode of End-of-Transmission (LP-11)
[TX-Side] Completes Transmission of payload data ->
[RX-Side] Receives payload data
[TX-Side] Toggles differential state immediately after last payload data bit and keeps that state for a time THSTRAIL
[TX-Side] Disables the HS-TX, enables the LP-TX, and drives Stop state (LP-11) for a time THS-EXIT
[RX-Side] Detects the Lines leaving LP-00 state and entering Stop state (LP-11) and disables Termination
[RX-Side] Neglect bits of last period THS-SKIP to hide transition effects
[RX-Side] Detect last transition in valid Data, determine last valid Data byte and skip trailer sequence
3. Lane States and Line Levels
Transmitter functions determine the Lane state by driving certain Line levels. During normal operation either a HS-TX or a LP-TX is driving a Lane. A HS-TX always drives the Lane differentially. The two LP-TX’s drive the two Lines of a Lane independently and single-ended. This results in two possible High-Speed Lane states and four possible Low-Power Lane states.The High-Speed Lane states are Differential-0 and Differential-1. The interpretation of Low-Power Lane states depends on the mode of operation.The LP-Receivers shall always interpret both High-Speed differential states as LP-00.
4 single-ended signal
Single-ended signaling is the simplest and most commonly used method of transmitting electrical signals over wires. One wire carries a varying voltage that represents the signal, while the other wire is connected to a reference voltage, usually ground.
The main alternative to single-ended signaling is called differential signaling. There is also the historic alternative of ground return, rarely used today.
Single ended signaling is less expensive to implement than differential, but it lacks the ability to reject noise caused by:
- differences in ground voltage level between transmitting and receiving circuits
- induction picked up on the signal wire
The main advantage of single-ended over differential signaling is that fewer wires are needed to transmit multiple signals. If there are n signals, then there are n+1 wires - one for each signal and one for ground. (Differential signaling uses at least 2n wires.) A disadvantage of single-ended signaling is that the return currents for all the signals share the same conductor (even if separate ground wires are used, the grounds are inevitably connected together at each end), and this can sometimes cause interference ("crosstalk") between the signals.
Single-ended signaling is widely used, and can be seen in numerous common transmission standards, including:
- RS-232 serial communications
- PS/2 mouse and keyboard connectors
- I²C serial bus
- TTL circuits
- CMOS logic circuits
- ECL circuits
- Most parallel computer buses, such as:
- VMEbus
- PCI
- VGA video connectors
- SCSI interfaces for hard drives and other peripherals
- Parallel ATA interfaces for hard drives and other peripherals
Some kinds of connectors, though more often used for balanced pairs, are sometimes used for single-ended operation:
- RCA jacks for audio signals
- TRS phone connectors for audio signals
Example
The widely used RS-232 system is an example of single-ended signaling, which uses ±12 V to represent a signal, and anything less than ±3 V to represent the lack of a signal. The high voltage levels give the signals some immunity from noise, since few naturally occurring signals can create a voltage of such magnitude. They also have the advantage of requiring only one wire per signal. However, they also have a serious disadvantage: they cannot run at high speeds. The effects of capacitance and inductance, which filter out high-frequency signals, limit the speed. Large voltage swings driving long cables also require significant power from the transmitting end. This problem can be reduced by using smaller voltages, but then the chance of mistaking random environmental noise for a signal becomes much more of a problem.
5 Differential signaling
Differential signaling is a method of transmitting information electrically with two complementary signals sent on two paired wires, called a differential pair. Since external interference tend to affect both wires together, and information is sent only by the difference between the wires, the technique improves resistance to electromagnetic noise compared with use of only one wire and an un-paired reference (ground). The technique can be used for both analog signaling, as in balanced audio, and digital signaling, as in RS-422, RS-485, Ethernet over twisted pair, PCI Express, DisplayPort, HDMI, and USB. The opposite technique is called single-ended signaling. Differential pairs are usually found on a printed circuit board, in cables (twisted-pair cables, ribbon cables), and in connectors.
Advantages
Tolerance of ground offsets
At the end of the connection, the receiving device reads the difference between the two signals. Since the receiver ignores the wires' voltages with respect to ground, small changes in ground potential between transmitter and receiver do not affect the receiver's ability to detect the signal.
Suitability for use with low-voltage electronics
In the electronics industry, and particularly in portable and mobile devices, there is a continuing tendency to lower the supply voltage in order to save power and reduce unwanted emitted radiation. A low supply voltage, however, causes problems with signaling because it reduces the noise immunity. Differential signaling helps to reduce these problems because, for a given supply voltage, it gives twice the noise immunity of a single-ended system.
To see why, consider a single-ended digital system with supply voltage . The high logic level is and the low logic level is 0 V. The difference between the two levels is therefore . Now consider a differential system with the same supply voltage. The voltage difference in the high state, where one wire is at and the other at 0 V, is . The voltage difference in the low state, where the voltages on the wires are exchanged, is . The difference between high and low logic levels is therefore . This is twice the difference of the single-ended system. Supposing that the voltage noise on one wire is uncorrelated to the noise on the other one, the result is that it takes twice as much noise to cause an error with the differential system as with the single-ended system. In other words, the noise immunity is doubled.
Resistance to electromagnetic interference
This advantage is not directly due to differential signaling itself, but to the common practice of transmitting differential signals on balanced lines.[1][2] Single-ended signals are still resistant to interference if the lines are balanced and terminated by a differential amplifier.
Comparison with single-ended signaling
In single-ended signaling, the transmitter generates a single voltage that the receiver compares with a fixed reference voltage, both relative to a common ground connection shared by both ends. In many instances single-ended designs are not feasible. Another difficulty is the electromagnetic interference that can be generated by a single-ended signaling system that attempts to operate at high speed.