Cray CRAY-1 - Page 182

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 broup 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-l 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.
Ready - The Ready signal sent from the CRAY-l 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 50% voltage points).
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-l to
show that the parcel was received and that the external device is
ready for the next parcel transmission. Resume is a pulse 50 ± 10
nanoseconds wide (at 50% voltage points).
Disconnect - Disconnect is a signal sent from the CRAY-l to the
external device
that means the transmission from the CRAY-l is
complete. It is sent after the CRAY-l has received the Resume
from the last Ready. The Disconnect is a pulse 50 ± 3 nanoseconds
wide (at 50% voltage points).
16-BIT HIGH-SPEED ASYNCHRONOUS CHANNELS
Input channels
Table 6-4
illustrates a general view of an input signal sequence.
Data Bits 2° through 2
15
- Data Bits 2°,2
1
,
... ,2
15
are signals
carrying a 16-bit parcel of data from the external device to the
CRAY-l. The data lines must be stable no later than 80 nanoseconds
after the leading edge of the associated Ready pulse and must be
held stable until at least 120 nanoseconds after the leading edge
of the same Ready. Note that if the device is transmitting at the
maximum allowable rate, it is normal for a data parcel to overlap
the subsequent
Ready pulse. Typically, data is transmitted 50 nsec
after the leading edge of Ready and held until 50 nsec after the
leading
edge of the following Ready pulse.
Parity Bits 0 through 3 - Parity Bits 0, 1, 2, and 3 are each a
parity bit assigned to a 4-bit group of data bits. The parity
bits are set or cleared to give the bit group odd parity.
2240004
6-10
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