Tandy 1000 SL Technical Reference Manual page 178

NEC
NEC Electronics Inc.
pPD765A/7265
SINGLE/DOUBLE DENSITY
FLOPPY DISK CONTROLLERS
Description
The pPD765A is an LSI floppy disk controller (FDC) chip
which contains the circuitry and control functions for
interfacing a processor to4 floppy diskdrives. It is capa-
ble of either IBM 3740 single density format (FM), or IBM
System
34
double density format (MFM) including
double-sided recording. The pPD765A 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 asso-
ciated with implementing a floppy disk interface.
The pPD7265 is an addition to the FDC family that has
been designed specifically for the Sony Micro Floppy-
disk" drive. ThepPD7265 is pincompatible and electri-
cally equivalent to the 765A but utilizes the Sony
recording format. The pPD7265 can read a diskette that
has been formatted by the pPD765A.
Each of these devices is also available in a -2 version.
The -2 versions represent a reduction from 4-micron to
Bmicron design rule. Functionality is the same. Minor
differences between the twoversions are detailed in the
AC Characteristics table. The -2 versions are only avail-
able in the plastic package at this time.
Hand-shaking signals are provided in the pPD765AI
pPD7265 which make DMA operation easy to incorpo-
rate with the aid of an external DMA controller chip,
such as the pPD8257. The FDC will operate in either the
DMA or non-DMA mode. In the non-DMA mode the FDC
generates interrupts to the processor every time a data
byte is to be transferred. In the DMA mode, the proces-
sor need only load the command into the FDC and all
data transfers occur under control of the FDC and DMA
controllers.
There are 15 commands which the pPD765AlpPD7265
will execute. Each of these commands requires multiple
&bit bytes to fully specify theoperation which the proc-
essor wishes the FDC to perform. The following com-
mands are available:
Read Data Read Deleted Data
Read ID Write Data
Specify Format Track
Read Track Write Deleted Data
Scan Equal Seek
Scan High or Equal Recalibrate
Scan Low or Equal Sense Interrupt Status
Sense Drive Status.
Features
Address mark detection circuitry is internal to the FDC
which simplifies the phase-locked loop and read elec-
tronics. The track stepping rate, head load time, and
head unload time are user-programmable. The
pPD765AlpPD7265 offers additional features such as
multi-track and multi-side read and write commands
and single and double density capabilities.
0 Sony (EMCA)-compatible recording format
bPD7265)
0 IBM-compatible format (single and double
density) bPD765A)
0 Multi-sector and multi-track transfer capability
0
Drive Up to 4 floppy or micro floppydlsk drives
0 Data scan capability- will scan a single sector or
an entire cylinder comparing byte-for-byte host
memory and disk data
0 Data transfers in DMA
or non-DMA mode
Parallel seek operations on up to four drives
0
Compatible with pPD8080/85, pPD8086/88 and
pPD780
(m)
microprocessors
0 Single-phase clock (8 MHz)
0 +5Vonly
ZBO is a registered trademark
of
the Zliog Corporation
Pin Configuration
6-3