The Percom Separator
The Radio Shack Expansion Interface added single-density floppy disk support to the TRS‑80 Model I. Floppy disks were a great improvement over cassettes. But many people reported problems with reliability, particularly when reading or writing lower disk tracks. CRC errors and locked out tracks occurred with disturbing regularity.
The Separator, sold by Percom for $29.95, fixed all of those problems. It provided a data separator with far higher resolution (16 MHz) than the separator used by the Expansion Interface (1 MHz). Good data separation was vital for isolating the clock and data pulses that made up a disk track.
More explanation of why this was so important was given in the Percom Separator manual:
The disk read data separation arrangement in the TRS‑80 Expansion Interface uses the internal data separator in the 1771 Disk Controller which is a part of the Expansion Interface. Use of the 1771 internal data separator is NOT RECOMMENDED by the 1771 manufacturer! The following note appears in the middle of page 17 of the Western Digital FD1771 data sheet:
NOTE: Internal data separation may work for some applications. However, for applications requiring high data recover reliability, WDC recommends external data separation be used.
Installation of the Separator required no soldering and only five steps:
- disassembling the Expansion Interface
- removing the floppy disk controller chip, a Western Digital 1771
- plugging the controller chip into the Percom Separator
- plugging the Percom Separator into the socket that previously housed the controller chip
- reassembling the Expansion Interface
The Separator was a popular item and Percom continued to sell it for many years. Its superior data separation was later integrated into Percom’s double-density add-on, the Percom Doubler.