Fibre Channel electrical interface
Encyclopedia
The Fibre Channel
electrical interface is one of two related standards that can be used to physically interconnect computer devices. The other standard is a Fibre Channel optical interface, which is not covered in this article.
differential interface. This usually consists of twisted-pair cables with a nominal impedance
of 75 ohm
s (single-ended) or 150 ohms (differential). This is a genuine differential signalling system so no ground reference is carried through the cable, except for the shield. Signalling is AC-coupled
, with the series capacitors located at the transmitter end of the link.
The definition of the Fibre Channel signalling voltage is complex. Eye-diagrams are defined for both the transmitter and receiver. There are many eye-diagram parameters which must all be met to be compliant with the standard. In simple terms, the transmitter circuit must output a signal with a minimum of 600 mV peak-to-peak differential, maximum 2000 mV peak-to-peak differential. A good signal looks rather like a sine-wave with a fundamental frequency of half the data rate, so 1 GHz for a typical system running at 2 gigabit
s per second.
The Bit-Error Rate (BER) objective for Fibre Channel systems is 1 in 1012 (1 bit in 1,000,000,000,000 bits). At 2 Gbit
/s this equates to seven errors per hour. Therefore, this is a common event and the receiver circuitry must contain error-handling logic. In order to achieve such a low error-rate, jitter "budgets" are defined for the transmitter and cables.
in use in the computer industry. Details of their pinout
s are distributed between different official documents. The following sections describe the most common Fibre Channel pinouts with some comments about the purpose of their electrical signals.
The most familiar Fibre Channel connectors are cable connectors, used for interconnects between initiators
and targets (usually disk enclosures). There are also "device connectors" that can be found on Fibre Channel disk-drives and backplanes of enclosures. The device connectors include pins for power and for setting disk options.
Optional pins 2, 3, 7, and 8 are intended for use with an external optical converter. This is often called a Media Interface Assembly (MIA).
Fibre channel DE-9 connectors often have only the 4 required contacts installed. Note that they are the four outermost contacts. This is an easy way to tell a fibre channel cable from an RS-232
cable.
Optional pins 2, 4, 5, and 7 are intended for use with an external optical converter. This is often called a Media Interface Assembly (MIA).
START options - if all the disks in an enclosure spin-up immediately on power-on, this can overload the power-supply. Two methods are available to avoid that problem:
DEVCTRL options - a disk that has the wrong interface speed can cause serious problems if it is inserted into an enclosure. That problem is avoided by providing three input pins to the disk that define the interface speed at which it will operate:
Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
electrical interface is one of two related standards that can be used to physically interconnect computer devices. The other standard is a Fibre Channel optical interface, which is not covered in this article.
Fibre Channel signal characteristics
Fibre channel electrical signals are sent over a duplexDuplex (telecommunications)
A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....
differential interface. This usually consists of twisted-pair cables with a nominal impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
of 75 ohm
Ohm
The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...
s (single-ended) or 150 ohms (differential). This is a genuine differential signalling system so no ground reference is carried through the cable, except for the shield. Signalling is AC-coupled
Capacitive coupling
In electronics, capacitive coupling is the transfer of energy within an electrical network by means of the capacitance between circuit nodes. This coupling can have an intentional or accidental effect...
, with the series capacitors located at the transmitter end of the link.
The definition of the Fibre Channel signalling voltage is complex. Eye-diagrams are defined for both the transmitter and receiver. There are many eye-diagram parameters which must all be met to be compliant with the standard. In simple terms, the transmitter circuit must output a signal with a minimum of 600 mV peak-to-peak differential, maximum 2000 mV peak-to-peak differential. A good signal looks rather like a sine-wave with a fundamental frequency of half the data rate, so 1 GHz for a typical system running at 2 gigabit
Gigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
s per second.
The Bit-Error Rate (BER) objective for Fibre Channel systems is 1 in 1012 (1 bit in 1,000,000,000,000 bits). At 2 Gbit
Gigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
/s this equates to seven errors per hour. Therefore, this is a common event and the receiver circuitry must contain error-handling logic. In order to achieve such a low error-rate, jitter "budgets" are defined for the transmitter and cables.
Fibre Channel connector pinouts
There are various Fibre Channel connectorsElectrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...
in use in the computer industry. Details of their pinout
Pinout
In electronics, a pinout is a cross-reference between the contacts, or pins, of an electrical connector or electronic component, and their functions.- Purpose :...
s are distributed between different official documents. The following sections describe the most common Fibre Channel pinouts with some comments about the purpose of their electrical signals.
The most familiar Fibre Channel connectors are cable connectors, used for interconnects between initiators
SCSI initiator
In computer data storage, a SCSI initiator is the endpoint that initiates a SCSI session, that is, sends a SCSI command. The initiator usually does not provide any Logical Unit Numbers ....
and targets (usually disk enclosures). There are also "device connectors" that can be found on Fibre Channel disk-drives and backplanes of enclosures. The device connectors include pins for power and for setting disk options.
9-pin "DE-9" cable connector
| Pin | Signal name | Comments |
| 1 | Fibre channel output | |
| 2 | Optional | |
| 3 | Module Fault Detect | Optional |
| 4 | Reserved | |
| 5 | Fibre channel input | |
| 6 | ||
| Fibre channel output | ||
| 7 | Output Disable | Optional |
| 8 | GND | Optional, return for pin 2 |
| 9 | ||
| Fibre channel input | ||
Optional pins 2, 3, 7, and 8 are intended for use with an external optical converter. This is often called a Media Interface Assembly (MIA).
Fibre channel DE-9 connectors often have only the 4 required contacts installed. Note that they are the four outermost contacts. This is an easy way to tell a fibre channel cable from an RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
cable.
8-pin "HSSDC" cable connector (High Speed Serial Data Connection)
| Pin | Signal name | Comments |
| 1 | Fibre channel output | |
| 2 | GND | Optional, return for pin 7 |
| 3 | ||
| Fibre channel output | ||
| 4 | Module Fault Detect | Optional |
| 5 | Output Disable | Optional |
| 6 | ||
| Fibre channel input | ||
| 7 | Optional | |
| 8 | Fibre channel input | |
Optional pins 2, 4, 5, and 7 are intended for use with an external optical converter. This is often called a Media Interface Assembly (MIA).
7-pin "HSSDC2" cable connector (High Speed Serial Data Connection)
| Pin | Signal name | Comments |
| 1 | GND |
| 2 | |
| Fibre channel output | |
| 3 | Fibre channel output |
| 4 | GND |
| 5 | Fibre channel input |
| 6 | |
| Fibre channel input | |
| 7 | GND |
40-pin "SCA-2" disk connector
Although SCA-2 is the official name for this connector, it is often called SCA-40 to distinguish it by its pin count from other similar connectors.| Pin | Signal name | Comments |
| 1 | ||
| Output driven high when port 1 is operating correctly | ||
| 2 | ||
| 3 | ||
| 4 | ||
| 5 | ||
| Input to allow ESI Enclosure Services Interface The Enclosure Services Interface is a computer protocol used in SCSI enclosures. This is part of a chain of connections that allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics... operation using the SELx pins |
||
| 6 | ||
| 7 | ACTLED | Output to drive the activity LED Light-emitting diode A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting... cathode |
| 8 | Power Control | |
| 9 | START1 | Input to control spin-up behavior (see the Disk options section) |
| 10 | START2 | Input to control spin-up behavior (see the Disk options section) |
| 11 | ||
| Output driven high when port 2 is operating correctly | ||
| 12 | SEL6 | Device ID bit 6 / ESI write clock |
| 13 | SEL5 | Device ID bit 5 / ESI read clock |
| 14 | SEL4 | Device ID bit 4 / ESI acknowledge clock |
| 15 | SEL3 | Device ID bit 3 / ESI bit 3 |
| 16 | FLTLED | Output to drive the fault LED cathode |
| 17 | DEVCTRL2 | Input to control interface speed (see the Disk options section) |
| 18 | DEVCTRL1 | Input to control interface speed (see the Disk options section) |
| 19 | ||
| 20 | ||
| 21 | ||
| 22 | GND (12V) | |
| 23 | GND (12V) | |
| 24 | Fibre channel input | |
| 25 | ||
| Fibre channel input | ||
| 26 | GND (12V) | |
| 27 | Fibre channel input | |
| 28 | ||
| Fibre channel input | ||
| 29 | GND (12V) | |
| 30 | Fibre channel output | |
| 31 | ||
| Fibre channel output | ||
| 32 | GND (5V) | |
| 33 | Fibre channel output | |
| 34 | ||
| Fibre channel output | ||
| 35 | GND (5V) | |
| 36 | SEL2 | Device ID bit 2 / ESI bit 2 |
| 37 | SEL1 | Device ID bit 1 / ESI bit 1 |
| 38 | SEL0 | Device ID bit 0 / ESI bit 0 |
| 39 | DEVCTRL0 | Input to control interface speed (see the Disk options section) |
| 40 | ||
Disk options
Some of the input signals to a Fibre Channel disk are used to control options, as follows:START options - if all the disks in an enclosure spin-up immediately on power-on, this can overload the power-supply. Two methods are available to avoid that problem:
| START1 | START2 | Spin-up behaviour |
| 0 | 0 | Automatic, immediate |
| 0 | 1 | Wait for Start Unit SCSI Start Stop Unit Command The SCSI Start/Stop Unit command is used to control the motor in a rotary device such as a SCSI disk-drive. It is also used to load or eject removable media, such as a tape or compact disc... SCSI command |
| 1 | 0 | Staggered, delayed depending on loop address |
| 1 | 1 | Reserved |
DEVCTRL options - a disk that has the wrong interface speed can cause serious problems if it is inserted into an enclosure. That problem is avoided by providing three input pins to the disk that define the interface speed at which it will operate:
| DEVCTRLx value | Interface speed |
| 0-4 | Reserved |
| 5 | 4 GB Gigabyte The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is... /s |
| 6 | 2 GB/s |
| 7 | 1 GB/s |