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ZX Interface 1: Difference between revisions
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Added Microdrive performance characteristics and Interface pinouts
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(Added Microdrive performance characteristics and Interface pinouts) |
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* ''Write Protect'' is raised when a writeable cartridge is present in the selected microdrive. | * ''Write Protect'' is raised when a writeable cartridge is present in the selected microdrive. | ||
* ''Gap'' and ''Sync'' are used to locate the correct block of data on the microdrive. | * ''Gap'' and ''Sync'' are used to locate the correct block of data on the microdrive. | ||
== Interface 1 Pin Assignments == | |||
The Interface 1 pin assignments contain 7 data pins, one of which is a high-voltage open-collector data pin, a 9v supply and several ground pins as well as a 2-pin keyway to avoid incorrect insertion. This is all configured as a 16 pin edge connector to connect to an IDC ( Insulation Displacement Connector ) plug. | |||
=== Microdrive Edge Connector === | |||
{| class="wikitable" style="text-align: center;" | |||
|- | |||
! rowspan="2" colspan="2" style="width: 8em;" | PIN | |||
! colspan="8" | Edge Connector | |||
|- | |||
! style="width: 5em;" | 15 | |||
! style="width: 5em;" | 13 | |||
! style="width: 5em;" | 11 | |||
! style="width: 5em;" | 09 | |||
! style="width: 5em;" | 07 | |||
! style="width: 5em;" | 05 | |||
! style="width: 5em;" | 03 | |||
! style="width: 5em;" | 01 | |||
|- | |||
! style="height: 8em;" rowspan="2" | Function | |||
! style="height: 4em;" | TOP | |||
| GND || GND || GND || ERASE || Comms Data || KEY ||Comms Clk || D1 | |||
|- | |||
! BOTTOM | |||
| GND || GND || GND || R/W || 9v || KEY ||WR-PROT || D0 | |||
|- | |||
! rowspan="2" colspan="2" style="width: 8em;" | PIN | |||
! style="width: 5em;" | 16 | |||
! style="width: 5em;" | 14 | |||
! style="width: 5em;" | 12 | |||
! style="width: 5em;" | 10 | |||
! style="width: 5em;" | 08 | |||
! style="width: 5em;" | 06 | |||
! style="width: 5em;" | 04 | |||
! style="width: 5em;" | 02 | |||
|- | |||
! colspan="8" | | |||
Viewed from side. | |||
|- | |||
|} | |||
Signals: | |||
* D0/D1 - Interleaved data, a byte at a time, from each of the read/write heads in the microdrive. Data rate approximately 80 Kbps per track. | |||
* Comms Clock - Drive select clock, identifies which drive to turn on. TTL level. | |||
* WR-PROT - A "low" on this indicates a cartridge is write protected. 9 volt = Not protected. | |||
* Comms Data - Drive select is serially clocked through drives. Logic 1 = selected. Line is inverted from register. | |||
* 9v - Power supply for drive, | |||
* ERASE - Open Collector via 270 Ohm resistor, to ERASE head on selected microdrive. | |||
* R/W - Write is active low. Select to read or write data to drive. | |||
== Microdrive Performance Characteristics == | |||
In many ways, the Microdrive, despite it's simple construction, performed similarly to disk systems of the era, and was roughly as fast at loading, however the lack of file allocation tables on the disk meant that the file allocation tables had to be build prior to every write operation, slowing down write access. | |||
* "Infinite loop" - Repeating magnetic tape. | |||
* Two tracks, operating as a single interleaved track. | |||
* Byte by byte interleave ( Even bytes Track 0, Odd bytes Track 1, Interleave every 4 bits. ) | |||
* Directoryless Data Structure. | |||
* Typical Capacity 90 Kb | |||
* 160 Kbps Data Transfer Rate ( 20 Kbytes/second raw transfer rate ) | |||
* Data encoded using Biphase Frequency Modulation ( same coding as credit card ) | |||
* Does not support a cartridge change line - All sectors must be eximined before writing data. | |||
* Typical full cycle time of around 8 to 10 seconds. | |||
* Can handle media stretching and data rate change without losing data. | |||
== Microdrive Data Storage Format == | |||
== External links == | == External links == | ||