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The CIU allows addressing any location in the GE-200 Series computer memory. The CIU
connects into any channel of the DATANET-30 buffer selector in the same manner as any other
DATANET-30 buffer.
The buffer selector address of CIU is specified by the wiring of the buffer
selector address plug for the CIU module.
There is no DATANET-30 hardware restriction on
the number of CIU's which may be used, other than the physical space occupied. On the computer
side, the CIU can connect into any plug of the GE-200 Series computer controller selector.
The computer interface unit can be tested for a Busy-Not Busy condition, by the DATANET-30.
This Busy-Not Busy test tells the DATANET-30 whether or not it can put data into the data
register and address register, and whether or not it can take data from the data and address
registers.
When the computer has traffic for the DATANET-30, the computer will set a flag in the computer
memory, which is interrogated by the DATANET-30. When the DATANET-30 is ready to accept
the traffic, a control instruction is sent to the computer, the computer program is interrupted,
and the traffic is transmitted under control of the DATANET-30. The DATANET-30 then pro-
cesses the traffic and sends it on to the remote station for which the traffic is intended. Thus
the computer and the DATANET-30 exchange control words, instructions and traffic under the
control of the DATANET-30.
RECEIVE SEQUENCE.
The following is a brief description of the operation of a CIU in the
receive mode; that is, taking words out of the GE-225 memory. Assume that nothing is happening
as far as the CIU is concerned. At some point, the program in the DATANET-30 decides to take
a block of words.
The program puts a number equal to one less than the initial address of the
block--the GE-225 address--in the address register of the CIU. Then the program sends a control
signal to the CIU which increases the address register by one, puts the CIU in the receive mode,
resets the data register, interrupts the GE-225 program for 1 word time, and initiates the transfer
of the word from the specified GE-225 memory location to the data register in the CIU. After the
word is in the data register, the CIU is no longer busy--this condition can be tested by the program.
The program now executes an instruction to take the word out of the data register of the CIU and
into the DATANET-30.
This instruction also increases the address in the CIU address register
by one, puts the CIU in the receive mode, resets the data register, and initiates the transfer of
another word from the GE-225 memory.
This process repeats until the DATANET-30 program
decides that sufficient words have been received.
TRANSMIT SEQUENCE. The following is a brief description of the operation of a CIU in the trans-
mit mode; that is, transferring words into the GE-225 memory. Assume that nothing is happening
as far as the CIU is concerned. At some point, the program in the DATANET-30 decides to put
a block of words into the GE-225.
The program puts a number equal to one less than the initial
address--the GE-225 address--in the address register of the CIU. Then the program transfers a
word into the CIU data register with an instruction. This instruction also puts the CIU in the
transmit mode, increases the address in the address register by one, interrupts the 225 program
for 1 word time, and initiates the transfer of the word from the data register into the GE-225
memory. After the word has been written in the GE-225 memory, the CIU is no longer busy. The
DATANET-30 program can now put another word in the data register and send it to the GE-225.
This process repeats until the DATANET-30 program decides that sufficient words have been
transferred.
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