Table 3-5 describes the signals on the ATA hard disk connector.
Table
3-5 Signals on the ATA hard disk connector
| Signal name |
Signal description |
| DA(0–2) |
Device address; used by the computer to select one of
the registers in the ATA drive. For more information, see the descriptions
of the CS0 and CS1 signals. |
| DD(0–15) |
Data bus; buffered from IOD(16–31) of the computer's
I/O bus. DD(0–15) are used to transfer 16-bit data to and from
the drive buffer. DD(8–15) are used to transfer data to and from the
internal registers of the drive, with DD(0–7) driven high when
writing. |
| /CBLID |
The host checks this signal after Power On or hardware
reset to detect whether an 80-conductor cable is present. |
| /CS0 |
Register select signal. It is asserted low to select
the main task file registers. The task file registers indicate the
command, the sector address, and the sector count. |
| /CS1 |
Register select signal. It is asserted low to select
the additional control and status registers on the ATA drive. |
| CSEL |
Cable select; not available on this computer (n.c.). |
| /DASP |
Device active or slave present; not available on this
computer (n.c.). |
| /DDMARDY |
Drive ready to receive Ultra DMA data. |
| /DIOR |
I/O data read strobe. |
| /DIOW |
I/O data write strobe. |
| /DMACK |
Used by the host to initiate a DMA transfer in response
to DMARQ. |
| DSTROBE |
Strobe for Ultra DMA data transfers to host. |
| /HDMARDY |
Ultra DMA data ready. |
| HSTROBE |
Strobe for Ultra DMA data transfers from host. |
| IORDY |
I/O ready; when driven low by the drive, signals the
CPU to insert wait states into the I/O read or write cycles. |
| /IOCS16 |
I/O channel select; not used on this computer (pulled
low by a 1 kilohm resistor). |
| DMARQ |
Asserted by the device when it is ready to transfer data
to or from the host. |
| INTRQ |
Interrupt request. This active high signal is used to
inform the computer that a data transfer is requested or that a
command has terminated. |
| /PDIAG |
Asserted by device 1 to indicate to device 0 that it
has completed the power-on diagnostics; not available on this computer
(n.c.). |
| /RESET |
Hardware reset to the drive; an active low signal. |
| Key |
This pin is the key for the connector. |
The built-in ATA devices are connected to the I/O bus through
bidirectional bus buffers.
