Megatel Quark/100 Specifications download pdf (Page 27)

drives.

AdditionalLy, a Side

Select

output

(SIDE)

provided

for

use with

double-sided

drives.

The

Select

and

SIDE

outputs are controlled

PBO,

2, 3,

and

4 of Port B

the

PIA.

These

lines are

initial

ized

act

outputs in the Bootstrap

PROM

routine.

The

Side Select line or

one

of the

Drive

Select lines

may

used as a

Low

Write-current

line.

Some

floppy disk drives require

external control line to reduce the write current

the

recording

head

when

writing

the

inner

tracks

the

diskette.

the

drives

connected

the

QUARK

require

such

a control

line,

then the system

installation

program

allows

any

of the Drive Select lines or the Side Select line to be

used

for

this

purpose.

Note

that

using a Drive Select line for

this

purpose

wou

reduce the

maxi

mum

number

of drives

that

could be connected to the

QUARK

three.

only single-sided drives are used, then the Side

Select

line

may

used

as the

Write-current line with

effect

the

maximum

number

fdrive~:r:h~:te~r:~·~~

allto~~he

drives connected

the

QUARK

must

the

same

size,

that

is,

that a combinat

of -inch

and

5.25-inch drives cannot be

directly

supported without a

modification to the ard. owever, since the

installation

merely

ties

the internal

Disk

/ Size Select line

low

(perm

tting

8-inch operation), a special control line connected

the

Disk

Size Select

line~can

used

change

the selected

Disk

Size under software control.

particular

appl i cation 0 the

QUARK

requi res

between

one

and

three 5.25-inch floppy disk

drives

and

only ale 8-inch

rive,

then the simplest solution

install

strap

from

the

Disk

Select

line

(SELO,

, or

which

used

select the 8-inch drive to the

Disk

Size Select line. Since tn Drive Select lines are active

low,

then

whenever

the 8-inch drive

selected, the

Disk

Size Select line

pulled

low,

enabl

ing

8-inch drive operation.

When

any

of the 5-inch drives are selected, the Drive Select line for the 8-inch drive,

and

thus

the

Disk

Size

Select

line,

will

logical

high

level,

putting

the

Floppy Disk

Interface into 5.25-inch operation,

just

requi red.

then

one

8-inch drive

to be

used

with

some

number

of 5.25-inch drives, then the

Disk

Size Select line

must

either

be connected to

unused

parallel

output line

from

the

PIA

VIA

the

QUARK

(which

can

be then controlled in a software patch

the

BIOS),

or the

Disk

Select lines

used

to select the 8-inch drives

must

AND-ed

together

and

the

result

this

combination

used

to control the

Disk

Size Select line.

The

latter

approach

ll,

of course,

require

external

AND

gate

well

the strap connecting the gate's output to the

Disk

Size

Select

line.

The

outputs

from

the

QUARK

the

fLoppy

disk drives are driven

medium-current low-

power

Schottky

TTL

drivers. Inputs

from

the floppy disk drives are terminated

1500hm

pullup

resistors

to the

+5V

supply

the

QUARK.

The

fLoppy

disk drive

most

distant

from

the

computer

should have

1500hm

terminating

pullups

the

output

lines

for

proper

transmission

line

characteristics.

None

of the intermediate drives should

have

passive loads

either

input or

output lines.

Most

of the remaining hardware for the

Floppy

Disk

Interface

incorporated within the

Western Digital

1793-02

Floppy

Disk

Controller (or equivalent).

Expansion

the Megatel

QUARK

Although

the various

members

of the Megatel

QUARK

family of single-board computers provide

all

of the functions necessary to integrate standard peripheral devices into a complete, stand-

alone

computer system,

there

may

special

additional

1/0

functions

needed in

some

applications.

The

QUARK

can accomodate

these

special

functions

through

its

Peripheral

Expansion Bus. This bus provides

external

access

the

eight

data

lines,

the

six

least-

significant

address

lines,

and

to appropriate timing

and

select

lines.

The

Read

<Rtn

and

Write

(iIR)

lines generated

the

Z80B

are brought out

the Peripheral

Expansion

Bus.

These

two

lines

would

used

with 8080-compatible peripheral devices,

such

the

8251

UART,

or the

8255

PPI.

connect

6500-

and

6800-compatible devices the E-clock

output

and

the W line are used.

For

these devices, the W line functions as the 6500/6800

RD/W

line.

Megatel

Computer

Technologies Toronto,

Canada

Page

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Megatel Quark/100 Specifications Page 27

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