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D765

Single/Double Density Floppy-Disk Controller

NEC => Renesas Technology 

NEC

uPD765A/uPD765B

Table 3. Status Register Identification (cont)

Pin

NC.

Name

Function

Status Register 3

D7 FT

(Fault)

This bit is used to indicate the status of the

fault signal from the FDD.

D6 WP

(Write Protected)

This bit is used to indicate the status of the

write protected signal from the FDD.

D56 RY

(Ready)

D4 TO

(Track 0)

This bit is used to Indicate the status of the

ready signal from the FDD.

This bit IS used to indicate the status of the

track 0 signal from the FDD.

03 TS

(Two-Side)

This bit IS used to indicate the status of the

two-side signal from the FDD.

D2 HD

(Head Address)

This bit is used to Indicate the status of the

side select signal to the FDD

D1

US1

(Unit Select 1)

This bit is used to Indicate the status of the

unit select 1 signal to the FDD.

D0 US0

(Unit Select 0)

This bit is used to indicate the status of the

unit select 0 signal to the FDD.

Note:

(1) CRC = Cyclic Redundancy Check

(2) IDR = Internal Data Register

(3) Cylinder (C) is described more fully in the Command Symbol

Description.

Command Sequence

The uPD765A/uPD765B is capable of performing 15 dif-

ferent commands. Each command is initiated by a

multibyte transfer from the processor, and the result af-

ter execution of the command may also be a multibyte

transfer back to the processor. Because of this multi-

byte interchange of information between the uPD765A/

uPD765B and the processor, it is convenient to consider

each command as consisting of three phases:

Command

Phase:

The FDC receives all information re-

quired to perform a particular opera-

tion from the processor.

Execution

Phase:

The FDC performs the operation it

was instructed to do.

Result Phase:

After completion of the operation,

status and other housekeeping infor-

mation are made available to the

processor.

Table 4 shows the required preset parameters and

results for each command. Most commands require 9

command bytes and return 7 bytes during the result

phase. The “W” to the left of each byte indicates a com-

mand phase byte to be written, and an “R” indicates a

result byte. The definitions of other abbriviations used

in table are given in the Command Symbol Description

table.

Command Symbol Description

Name

Function

A0

(Address Line 0)

A0 controls selection of main status register

(A0=0) or data register (A0= 1).

C

(Cylmder Number)

C stands for the current /selected cylinder

(track) numbers 0 through 76 of the medium

D

(Data)

D stands for the data pattern which is going to be

written into a sector during WRITE ID operation

D7-D0

(Data Bus)

8-bit data bus, where D7 stands for a most

significant bit, and D0 s t a n d s f o r a l e a s t

significant bit.

DTL

(Data Length)

When N is defined as 00. DTL stands for the data

length which users are going to read out or write

into the sector

EOT

(End of Track)

EOT stands for the final sector number on a cylin-

der Durmg read or write operations, FDC will stop

data transfer after a sector number equal to EOT

GPL

(Gap Length)

GPL stands for the length of gap 3. During Read /

Write commands this value determines the num-

ber of bytes that VCO sync will stay low after two

CRC bytes During Format command it deter-

mines the size of gap 3

H

(Head Address)

H stands for the logical head number 0 or 1. as

specified in ID field

HD (Head)

HD stands for a the physical head number 0 or 1

and controls the polarity of pin 27 (H = HD in all

command words )

HLT

(Head Load Time)

HLT stands for the head load time in the FDD (2 to

254 ms in 2 ms Increments).

HUT

(Head Unload Time)

HUT stands for the head unload time after a Read

or Write operation has occurred (16 to 240 ms in

16 ms Increments)

MF

(FM or MFM Mode)

If MF IS low, FM mode IS selected, and if it is high,

MFM mode IS selected

MT

(Multitrack)

IF MT is high, a multitrack operation IS per-

formed If MT = 1 after finishing read/write oper-

ation on siude 0. FDC will automatically start

searching for sector 1 on side 1

N

(Number)

N stands for the number of data bvtes written in a

sector

NCN

(New Cylinder Number)

NCN stands for a new cylinder number which is

going to be reached as a result of the seek opera-

tion; desired position of head

ND

(Non-DMA Mode)

ND stands for operation in the non-DMA mode

PCN

PCN stands for the cylinder number at the

(Present Cylinder Number) completion of Sense Interrupt Status command,

position of head at present time

R

[Record)

R stands for the sector number which will be read

or written

R/W

(Read/Write)

R/W stands for either Read (R) or Write (W)

signal

SC

(Sector)

SC indicates the number of sectors per cylinder

SK

(Skip)

SK stands for skip deleted data address mark

5-13

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