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NEe
NEe Microcomputers, Inc. fLPD765


SINGLE/DOUBLE DENSITY
FLOPPY DISK CONTROLLER'


OESCRI PTION The J.1PD765 is an LSI Floppy Disk Controller (FDC) Chip, which contains the circuitry and control
functions for interfacing a processor to 4 Floppy Disk Drives, It is capable of supporting either
IBM 3740 single density format (FM), or IBM System 34 Double Density format (MFM) including
double sided recording. The J.1PD765 provides control signals which simplify the design of an
external phase locked loop, and write precompensation circuitry. The FDC simplifies and handles
most of the burdens associated with implementing a Floppy Disk Interface.
Hand-shaking signals are provided in the J.1PD765 which make DMA operation easy to incorporate
with the aid of an external DMA Controller chip, such as the J.1PD8257. The FDC will operate in
either DMA or Non-DMA mode. In the Non-DMA mode, the FDC generates interrupts to the
processor every time a data byte is available. In the DMA mode, the processor need only load the
command into the FDC and all data transfers occur under control of the J.1PD765 and DMA
controller.
There are 15 separate commands which the J.1PD765 will execute. Each of these commands requ ire
multiple 8-bit bytes to fully specify the operation which the processor wishes the F DC to perform.
The following commands are available:
Read Data Scan High or Equal Write Deleted Data
Read ID Scan Low or Equal Seek
Read Deleted Data Specify Recalibrate (Restore to Track 0)
Read a Track Write Data Sense I nterrupt Status
Scan Equal Format a Track Sense Drive Status

FEATURES Address mark detection circuitry is internal to the FDC which simplifies the phase locked loop and
read electronics. The track stepping rate, head load time, and head unload time may be programmed
by the user. The J.1PD765 offers many additional features such as multiple sector transfers in both
read and write with a single command, and full IBM compatibil ity in both single and double
density modes.