Upgrading and Repairing PCs

ATA Features

The ATA standards have gone a long way toward eliminating incompatibilities and problems with interfacing IDE drives to ISA/PCI bus systems. The ATA specifications define the signals on the 40-pin connector, the functions and timings of these signals, cable specifications, and so on. The following section lists some of the elements and functions defined by the ATA specification.

ATA I/O Connector

The ATA interface connector is normally a 40-pin header-type connector with pins spaced 0.1'' (2.54mm) apart, and generally it is keyed to prevent the possibility of installing it upside down (see Figures 7.2 and 7.3). To create a keyed connector, the manufacturer usually removes pin 20 from the male connector and blocks pin 20 on the female cable connector, which prevents the user from installing the cable backward. Some cables also incorporate a protrusion on the top of the female cable connector that fits into a notch in the shroud surrounding the mating male connector on the device. The use of keyed connectors and cables is highly recommended. Plugging in an ATA cable backward normally won't cause any permanent damage; however, it can lock up the system and prevent it from running at all.

Table 7.3 shows the standard 40-pin ATA (IDE) interface connector pinout.

Table 7.3. 40-Pin ATA Connector

Signal Name	Pin	Pin	Signal Name
-RESET	1	2	GROUND
Data Bit 7	3	4	Data Bit 8
Data Bit 6	5	6	Data Bit 9
Data Bit 5	7	8	Data Bit 10
Data Bit 4	9	10	Data Bit 11
Data Bit 3	11	12	Data Bit 12
Data Bit 2	13	14	Data Bit 13
Data Bit 1	15	16	Data Bit 14
Data Bit 0	17	18	Data Bit 15
GROUND	19	20	KEY (pin missing)
DRQ 3	21	22	GROUND
-IOW	23	24	GROUND
-IOR	25	26	GROUND
I/O CH RDY	27	28	CSEL:SPSYNC[1]
-DACK 3	29	30	GROUND
IRQ 14	31	32	Reserved[2]
Address Bit 1	33	34	-PDIAG
Address Bit 0	35	36	Address Bit 2
-CS1FX	37	38	-CS3FX
-DA/SP	39	40	GROUND
+5V (Logic)	41	42	+5V (Motor)
GROUND	43	44	Reserved
Note that "-" preceding a signal name (such as with -RESET) indicates the signal is "active low."

^[1] Pin 28 is usually cable select, but some older drives could use it for spindle synchronization between multiple drives.

^[2] Pin 32 was defined as -IOCS16 in ATA-2 but is no longer used.

The 2 1/2'' drives found in notebook/laptop-size computers typically use a smaller unitized 50-pin header connector with pins spaced only 2.0mm (0.079'') apart. The main 40-pin part of the connector is the same as the standard ATA connector (except for the physical pin spacing), but there are added pins for power and jumpering. Normally, the cable that plugs into this connector has 44 pins, carrying power as well as the standard ATA signals. The jumper pins usually have a jumper on them (the jumper position controls cable select, master, or slave settings). Figure 7.4 shows the unitized 50-pin connector used on 2 1/2'' ATA drives found in laptop or notebook computers.

Note the jumper pins at positions A–D and that the pins at positions E and F are removed. A jumper usually is placed between positions B and D to set the drive for cable select operation. On this connector, pin 41 provides +5v power to the drive logic (circuit board), pin 42 provides +5v power to the motor (2 1/2'' drives use 5v motors, unlike larger drives that typically use 12v motors), and pin 43 provides a power ground. The last pin (44) is reserved and not used.

Table 7.4 shows the 50-pin unitized ATA interface connector pinout as used on most 2 1/2'' (laptop or notebook computer) drives.

Table 7.4. 50-Pin Unitized ATA 2 1/2'' (Notebook/Laptop Drive) Connector Pinout

Signal Name	Pin	Pin	Signal Name
Jumper pin	A	B	Jumper pin
Jumper pin	C	D	Jumper pin
KEY (pin missing)	E	F	KEY (pin missing)
-RESET	1	2	GROUND
Data Bit 7	3	4	Data Bit 8
Data Bit 6	5	6	Data Bit 9
Data Bit 5	7	8	Data Bit 10
Data Bit 4	9	10	Data Bit 11
Data Bit 3	11	12	Data Bit 12
Data Bit 2	13	14	Data Bit 13
Data Bit 1	15	16	Data Bit 14
Data Bit 0	17	18	Data Bit 15
GROUND	19	20	KEY (pin missing)
DRQ 3	21	22	GROUND
-IOW	23	24	GROUND
-IOR	25	26	GROUND
I/O CH RDY	27	28	CSEL
-DACK 3	29	30	GROUND
IRQ 14	31	32	Reserved
Address Bit 1	33	34	-PDIAG
Address Bit 0	35	36	Address Bit 2
-CS1FX	37	38	-CS3FX
-DA/SP	39	40	GROUND
+5v (Logic)	41	42	+5V (Motor)
GROUND	43	44	Reserved

Not All Cables and Connectors Are Keyed Many lower-cost board and cable manufacturers leave out the keying. Cheaper motherboards often won't have pin 20 removed on their ATA connectors, and consequently they won't supply a cable with pin 20 blocked. If they don't use a shrouded connector with a notch and a corresponding protrusion on the cable connector, no keying exists and the cables can be inserted backward. Fortunately, the only consequence of this in most cases is that the device won't work until the cable is attached with the correct orientation. Note that some systems will not display any video until the ATA drives respond to a spin-up command, which they can't receive if the cable is connected backward. So, if you connect an unkeyed ATA drive to your computer, turn on the computer, and it seems as if the system is locked up (you don't see anything on the screen), check the ATA cable. (See Figure 7.6 for examples of unkeyed and keyed ATA cables.) Figure 7.6. 40-wire (left) and 80-wire (right) ATA cables. In rare situations in which you are mixing and matching items, you might encounter a cable with pin 20 blocked (as it should be) and a board with pin 20 still present. In that case, you can break off pin 20 from the board—or for the more squeamish, remove the block from the cable or replace the cable with one without the blocked pin. Some cables have the block permanently installed as a part of the connector housing, in which case you must break off pin 20 on the board or device end or use a different cable. The simple rule of thumb is that pin 1 should be oriented toward the power connector on the device, which normally corresponds to the stripe on the cable.

ATA I/O Cable

A 40-conductor ribbon cable is specified to carry signals between the bus adapter circuits and the drive (controller). To maximize signal integrity and eliminate potential timing and noise problems, the cable should not be longer than 18'' (0.46 meters).

Note that ATA drives supporting the higher-speed transfer modes, such as PIO Mode 4 or any of the Ultra-DMA (UDMA) modes, are especially susceptible to cable integrity problems and cables that are too long. If the cable is too long, you can experience data corruption and other errors that can be maddening. This will be manifested in any type of problem reading from or writing to the drive. In addition, any drive using UDMA Mode 5 (66MBps transfer rate), Mode 6 (100MBps transfer rate), or Mode 7 (133MBps transfer rate) must use a special, higher-quality 80-conductor cable (the extra conductors are grounds to reduce noise). I also recommend this type of cable if your drive is running at UDMA Mode 2 (33MBps) or slower because it can't hurt and can only help. I always keep a high-quality 80-conductor ATA cable in my toolbox for testing drives where I suspect cable integrity or cable length problems. Figure 7.5 shows the typical ATA cable layout and dimensions.

Note Most 40-conductor cables do not color-code the connectors, whereas all 80-conductor cables do color-code the connectors.

Two primary variations of ATA cables are used today: one with 40 conductors and the other with 80 conductors (see Figure 7.6). Both use 40-pin connectors, and the additional wires in the 80-conductor version are simply wired to ground. The additional conductors are designed to reduce noise and interference and are required when setting the interface to run at 66MBps (ATA/66) or faster. The drive and host adapter are designed to disable the higher-speed ATA/66, ATA/100, or ATA/133 modes if an 80-conductor cable is not detected. In such cases, you might see a warning message when you start your computer if an ATA/66 or faster drive is connected to a 40-wire cable. The 80-conductor cable can also be used at lower speeds; although this is unnecessary, it improves the signal integrity. Therefore, it is the recommended version no matter which drive you use.

I once had a student ask me how to tell an 80-conductor cable from a 40-conductor cable. I thought to myself, "Is this a trick question?" Perhaps he didn't know that each conductor in a ribbon cable can be seen as a rib or ridge in the cable. The simple answer is to count the ridges (conductors) in the cable. If you count only 40, it must be a 40-conductor cable, and if you count to 80, well…you get the idea! If you observe them side by side, the difference is clear: The 80-conductor cable has an obviously smoother, less ridged appearance than the 40-conductor cable.

Note the keying on the 80-wire cable that is designed to prevent backward installation, but note also that the poorly constructed 40-wire cable shown in this example lacks keying. Most good 40-conductor cables include the keying; however, because it is optional, many cheaply constructed versions do not include it. Keying was made mandatory for all 80-conductor cables as part of the standard.

ATA Signals

This section describes some of the most important ATA signals having to do with drive configuration and installation in more detail. This information can help you to understand how the cable select feature works, for example.

Pin 20 is used as a key pin for cable orientation and is not connected to the interface. This pin should be missing from any ATA connectors, and the cable should have the pin-20 hole in the connector plugged off to prevent the cable from being plugged in backward.

Pin 39 carries the drive active/slave present (DASP) signal, which is a dual-purpose, time-multiplexed signal. During power-on initialization, this signal indicates whether a slave drive is present on the interface. After that, each drive asserts the signal to indicate that it is active. Early drives could not multiplex these functions and required special jumper settings to work with other drives. Standardizing this function to allow for compatible dual-drive installations is one of the features of the ATA standard. This is why some drives require a slave present (SP) jumper whereas others do not.

Pin 28 carries the cable select signal (CSEL). In some older drives, it could also carry a spindle synchronization signal (SPSYNC), but that is not commonly found on newer drives. The CSEL function is the most widely used and is designed to control the designation of a drive as master (drive 0) or slave (drive 1) without requiring jumper settings on the drives. If a drive sees the CSEL as being grounded, the drive is a master; if CSEL is open, the drive is a slave.

You can install special cabling to ground CSEL selectively. This installation usually is accomplished through a Y-cable arrangement, with the ATA bus connector in the middle and each drive at opposite ends of the cable. One leg of the Y has the CSEL line connected through, indicating a master drive; the other leg has the CSEL line open (conductor interrupted or removed), making the drive at that end the slave.

Dual-Drive Configurations

Dual-drive ATA installations can be problematic because each drive has its own controller and both controllers must function while being connected to the same bus. There has to be a way to ensure that only one of the two controllers will respond to a command at a time.

The ATA standard provides the option of operating on the AT bus with two drives in a daisy-chained configuration. The primary drive (drive 0) is called the master, and the secondary drive (drive 1) is called the slave. You designate a drive as being master or slave by setting a jumper or switch on the drive or by using a special line in the interface called the cable select (CS) pin and setting the CS jumper on the drive.

When only one drive is installed, the controller responds to all commands from the system. When two drives (and, therefore, two controllers) are installed, both controllers receive all commands from the system. Each controller then must be set up to respond only to commands for itself. In this situation, one controller must be designated as the master and the other as the slave. When the system sends a command for a specific drive, the controller on the other drive must remain silent while the selected controller and drive are functioning. Setting the jumper to master or slave enables discrimination between the two controllers by setting a special bit (the DRV bit) in the Drive/Head Register of a command block.

Configuring ATA drives can be simple, as is the case with most single-drive installations, or troublesome, especially when it comes to mixing two older drives from different manufacturers on a single cable.

Most ATA drives can be configured with four possible settings:

• Master (single-drive)

• Master (dual-drive)

• Slave (dual-drive)

• Cable select

Many drives simplify this to three settings: master, slave, and cable select. Because each ATA drive has its own controller, you must specifically tell one drive to be the master and the other to be the slave. No functional difference exists between the two, except that the drive that's specified as the slave will assert a signal called DASP after a system reset informs the master that a slave drive is present in the system. The master drive then pays attention to the drive select line, which it otherwise ignores. Telling a drive that it's the slave also usually causes it to delay its spinup for several seconds to allow the master to get going and thus to lessen the load on the system's power supply.

Until the ATA specification, no common implementation for drive configuration was in use. Some drive companies even used different master/slave methods for different models of drives. Because of these incompatibilities, some drives work together only in a specific master/slave or slave/master order. This situation mostly affects older IDE drives introduced before the ATA specification.

Most drives that fully follow the ATA specification now need only one jumper (master/slave) for configuration. A few also need a slave present jumper, as well. Table 7.5 shows the jumper settings required by most ATA drives.

Table 7.5. Jumper Settings for Most ATA-Compatible Drives on Standard (Non–Cable Select) Cables

Jumper Name	Single-Drive	Dual-Drive Master	Dual-Drive Slave
Master (M/S)	On	On	Off
Slave Present (SP)	Off	On	Off
Cable Select (CS)	Off	Off	Off

Note If a cable select cable is used, the CS jumper should be set On and all others should be Off. The cable connector then determines which drive will be master or slave.

Figure 7.7 shows the jumpers on a typical ATA drive.

The master jumper indicates that the drive is a master or a slave. Some drives also require a slave present jumper, which is used only in a dual-drive setup and then installed only on the master drive—which is somewhat confusing. This jumper tells the master that a slave drive is attached. With many ATA drives, the master jumper is optional and can be left off. Installing this jumper doesn't hurt in these cases and can eliminate confusion; I recommend that you install the jumpers listed here.

Note Note that some drives have these jumpers on the drive circuit board on the bottom of the drive, and as such they might not be visible on the rear.

To eliminate confusion over master/slave settings, most newer systems now use the cable select option. This involves two things. The first is having a special ATA cable that has all the wires except pin 28 running from the motherboard connector to both drive connectors. Pin 28 is used for cable select and is connected to one of the drive connectors (labeled master) and not to the other (labeled slave). Both drives are then configured in cable select mode via the CS jumper on each drive.

With cable select, the drive that receives signals on pin 28 automatically becomes the master, and the other becomes the slave. Most cables implement this by removing the metal insulation displacement bit from the pin-28 hole, which can be difficult to see at a glance. Other cables have a section of pin 28 visibly cut from the cable somewhere along the ribbon. Because this is such a minor modification to the cable and can be difficult to see, cable select cables typically have the connectors labeled master, slave, and system, indicating that the cable controls these options rather than the drive. All 80-conductor UltraATA cables are designed to use cable select.

With cable select, you simply set the CS jumper on all drives and then plug the drive you want to be the master into the connector labeled master on the cable and the drive you want to be the slave into the connector labeled slave.

The only downside I see to using cable select is that it can restrict how the cable is routed or where you mount the drive that is to be master versus slave because they must be plugged into specific cable connector positions.

ATA Commands

One of the best features of the ATA (also known as IDE) interface is the enhanced command set. The ATA interface was modeled after the WD1003 controller IBM used in the original AT system. All ATA drives must support the original WD command set (eight commands) with no exceptions, which is why ATA drives are so easy to install in systems today. All IBM-compatible systems have built-in ROM BIOS support for the WD1003, so they essentially support ATA as well.

In addition to supporting all the WD1003 commands, the ATA specification added numerous other commands to enhance performance and capabilities. These commands are an optional part of the ATA interface, but several of them are used in most drives available today and are very important to the performance and use of ATA drives in general.

Perhaps the most important is the Identify Drive command. This command causes the drive to transmit a 512-byte block of data that provides all details about the drive. Through this command, any program (including the system BIOS) can find out exactly which type of drive is connected, including the drive manufacturer, model number, operating parameters, and even the serial number of the drive. Many modern BIOSes use this information to automatically receive and enter the drive's parameters into CMOS memory, eliminating the need for the user to enter these parameters manually during system configuration. This arrangement helps prevent mistakes that can later lead to data loss when the user no longer remembers what parameters he used during setup.

The Identify Drive data can tell you many things about your drive, including the following:

• Number of logical block addresses available using LBA mode

• Number of physical cylinders, heads, and sectors available in P-CHS mode

• Number of logical cylinders, heads, and sectors in the current translation L-CHS mode

• Transfer modes (and speeds) supported

• Manufacturer and model number

• Internal firmware revision

• Serial number

• Buffer type/size, indicating sector buffering or caching capabilities

Several public-domain programs can execute this command to the drive and report the information onscreen. In the past, I've used the IDEINFO program available at (http://www.tech-pro.co.uk/ideinfo.html). However, because this program was created almost a decade ago, it doesn't provide the best information about recent drives. For more up-to-date information, use IDEDIAG, which is available from http://www.penguin.cz/~mhi/idediag, or HWINFO, which is available from http://www.hwinfo.com. (I find these programs especially useful when I am trying to install ATA drives on a system that has a user-defined drive type but doesn't support autodetection and I need to know the correct parameters for a user-definable BIOS type. These programs get the information directly from the drive.)

Two other important commands are the Read Multiple and Write Multiple commands. These commands permit multiple-sector data transfers and, when combined with block-mode PIO capabilities in the system, can result in incredible data-transfer rates many times faster than single-sector PIO transfers. Some older systems require you to select the correct number of sectors supported by the drive, but most recent systems automatically determine this information for you.

Many other enhanced commands are available, including room for a given drive manufacturer to implement what are called vendor-unique commands. Certain vendors often use these commands for features unique to that vendor. Often, vendor-unique commands control features such as low-level formatting and defect management. This is why low-level format programs can be so specific to a particular manufacturer's ATA drives and why many manufacturers make their own LLF programs available.