ESI Electrical Interface
The ESI interface was designed to make use of the seven existing "SEL_n" address signals which are used at power-on time for establishing the address (ALPA) of a disk-drive. An extra eighth signal called "-PARALLEL ESI" is used to switch the function of the SEL_n signals.
| Signal name | Function |
| SEL_0/D0 | Data bus bit 0 |
| SEL_1/D1 | Data bus bit 1 |
| SEL_2/D2 | Data bus bit 2 |
| SEL_3/D3 | Data bus bit 3 |
| SEL_4/-ENCL_ACK | The enclosure clocks this to acknowledge a read or write data transfer |
| SEL_5/-DSK_RD | The disk-drive clocks this to send a NIBL of data to the enclosure |
| SEL_6/-DSK_WR | The disk-drive clocks this to receive a NIBL of data from the enclosure |
Read more about this topic: Enclosure Services Interface
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