Cray CRAY-1 - Page 185

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I

Parity

Bits 0 through 3 -

Parity

Bits 0, 1, 2,

and

3 are each assigned

to a

4-bit

group of data

bits.

The

parity

bits

are

set

or cleared to

give the

bit

group

odd

parity.

Bit assignments are

as

follows:

Parity

Bit

0

Data

Bits

20

- 2

3

Parity

Bit 1

Data

Bits

24

-

27

Parity

Bit

2

Data

Bits 2

8

-

211

Parity

Bit 3

Data

Bits

212

- 2

15

Parity

bits

are

sent

from

the

CRAY-1

to the external device

at

the

same

time as the data

bits.

They

are held

stable

in the

same

way

as

are the data

bits.

Channel

Master Clear -

The

Channel

Master Clear

may

be

programmed

(see description of

Programmed

Master Clear

later

in

this

section)

or

may

the

result

of a Clear

I/O

signal.

The

Master Clear signal

may

be

used

by

the external devices

for

control purposes or

may

be

ignored.

Ready

-

The

Ready

signal sent

from

the

CRAY-1

to the external device

indicates

that

the data

is

present

and

may

be

sampled.

The

Ready

signal

is

a pulse

50

± 3 nanoseconds

wide

(at

the

50%

voltage points)

sent in groups

of

four.

For

any

group

of

Ready

pulses, the time

from

the leading

edge

of

one

Ready

to the leading

edge

of

the

next

Ready

is

100

± 3 nanoseconds.

The

leading

edge

of

Ready

may

be

used

to time data sampling in the external device.

Resume

-

Resume

is

sent

from

the external device to the

CRAY-1

to

show

that

the

64-bit

word

of four parcels

was

received

and

that

the

external device

is

ready

for

the next

word

(four

parcels).

Resume

is

a pulse

50

±

10

nanoseconds

wide

(at

the

50%

voltage

points).

The

pulse

must

be

received

at

the

CRAY-1

no

earlier

than

230

nanoseconds

after

the leading

edge

of the

first

Ready

pulse

is

transmitted.

Disconnect - Disconnect

is

a signal

sent

from

the

CRAY-1

to the

external device

that

means

the transmission

from

the

CRAY-1

is

complete.

It

is

sent with the

last

Ready

± 3 nanoseconds.

The

Disconnect pulse

is

50

± 3 nanoseconds

wide

(at

the

50%

voltage pOints).

16-BIT

SYNCHRONOUS

CHANNELS

Input channels

Table 6-6

illustrates

a general

view

of

an

input signal sequence.

Data

Bits

20

through 2

15

-

Data

Bits 20, 2

1

,

...

,2

15

are

signals

carrying a

16-bit

parcel of data

from

the external device to the

CRAY-1.

They

are

all

valid

within 5 nanoseconds

of

each

other.

Data

Bit

signals

must

remain unchanged

on

the

lines

until

the next

parcel

is

sent.

2240004

6-13

E

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