uPD765A/uPD765B

NEC

Table 3. Status Register Identification (cont)

Command Symbol Description

Name

A0

(Address Line 0)

C

(Cylmder Number)

D

(Data)

D7-D0

(Data Bus)

DTL

(Data Length)

Function

A0 controls selection

of main status register

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

C stands for the current /selected cylinder

(track) numbers 0 through 76 of the medium

D stands for the data pattern which

is going to be

written into a sector during WRITE ID operation

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

significant bit, and D0 stands for a least

significant bit.

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

length which users are going to read out or write

into the sector

Pin

NC.

Name

Function

Status Register 3

D7

FT

This bit is used to indicate the status of the

fault signal from the FDD.

This bit is used to indicate the status of the

(Fault)

D6

WP

(Write Protected)

write protected signal from the FDD.

D56

RY

This bit is used to Indicate the status of the

(Ready)

D4

TO

(Track 0)

03

TS

ready signal from the FDD.

indicate

the

track 0 signal from the FDD.

(Two-Side)

D2

HD

two-side signal from the FDD.

This bit is used to Indicate the

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

EOT

(End of Track)

(Head Address)

D1

US1

(Unit Select 1)

D0

US0

(Unit Select 0)

Note:

side select signal to the FDD

This bit is used to Indicate the status of the

unit select 1 signal to the FDD.

This bit is used to indicate the status of the

unit select 0 signal to the FDD.

(1) CRC = Cyclic Redundancy Check

(2) IDR = Internal Data Register

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

Description.

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 stands for the logical

head number 0 or 1. as

specified

in ID field

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

254 ms in 2 ms Increments).

HUT stands for the head unload time after a Read

or Write operation has occurred (16 to 240 ms in

16 ms Increments)

H

(Head Address)

HD(Head)

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:

HLT

(Head Load Time)

HUT

(Head Unload Time)

MF

(FM or MFM Mode)

MT

(Multitrack)

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

ation on siude 0. FDC will automatically

start

searching for sector 1 on side 1

Command

Phase:

Execution

Phase:

Result Phase:

The FDC receives all information re-

quired to perform a particular opera-

tion from the processor.

The FDC performs the operation it

was instructed to do.

After

completion

of

the

operation,

status and other housekeeping infor-

mation

are

made

available

to

the

processor.

N

N stands for the number of data bvtes written in a

(Number)

sector

NCN

NCN stands for a new cylinder number which

is

(New Cylinder Number)

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

tion; desired position

of head

ND

ND stands for operation in the non-DMA mode

(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

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.

R

[Record)

R/W

(Read/Write)

SC

(Sector)

SK

(Skip)

R stands for the sector number which

will be read

or written

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

signal

SC indicates the number of sectors per cylinder

SK stands for skip deleted data address mark

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