Data Transfer; Datanet-30 To The Computer Interface Unit; External Computer To The Computer Interface Unit; Data Flow Through The Computer Interface Unit - GE DATANET-30 System Manual

Data Transfer
Data is transferred in both
dire(t'~ut
only in one direction at a time. Control of the direction
of data flow is established and maintained by either the external computer or the DATANET-30,
Should both the DAT AN ET-30 and the external computer desire control at exactly the same time,
the external computer is given priority.
The CIU has an 18-bit buffer. Data is transferred one character at a time to or from the external
computer and one DATANET-30 word at a time to or from the DATANET-30. The CIU contains
the necessary shift circuitry to accumulate characters into words and separate sequential
characters, depending on the direction of data transfer. Data transfer is illustrated in Figure 23.
DATANET-30
CIU
6
Bits +
18 Bits, No Parity ..
Ocid Parity
.
Parity
Generated
CIU
6
Bits +
-- 18 Bits, No Parity
--
Odd Parity
--
Checks and
Removes Parity
Figure 23. Data Transfer Through a CIU 931
-
External
Computer
DATANET-30 TO THE COMPUTER INTERFACE UNIT. When the CIU has received a word from
the DATANET-30, a signal for the external computer to read is generated. The external computer
initiates the transfer of one character at a time from the CIU. When the three characters have
been transferred, the CIU notifies the DATANET-30 that another word can be transferred. The
DATANET-30 program then transfers another word to the CIU. This process continues until
the DATANET-30 or external computer sends an End Data Transfer signal to the CIU.
EXTERNAL COMPUTER TO THE COMPUTER INTERFACE UNIT. When the CIU has received
three characters from the external computer, a signal for the DATANET-30 to transfer the three
characters is sent to the DATANET-30. The DATANET-30 program must detect this signal and
transfer the data from the CIU. When the data has been transferred from the CIU, the external
computer can transfer three more characters to the CIU. This process continues until the
external computer or DATANET-30 sends an End Data Transfer signal to the CIU.
DATA FLOW THROUGH THE COMPUTER INTERFACE UNIT. When data is transferred from the
CIU to the external computer, the most significant character of the DATANET-30 word is trans-
ferred first and the least significant last.
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