IMP-Host interface flow diagrams
RFC 12

Document Type RFC - Unknown (August 1969; No errata)
Last updated 2014-05-06
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Network Working Group                                       M. Wingfield
Request for Comments: 12  REVISED                         26 August 1969

                    IMP-HOST INTERFACE FLOW DIAGRAMS

   The following flow diagrams were extracted from the logic diagrams
   provided in Appendix B of BBN Report No. 1822.  These diagrams
   indicate the logical sequence of hardware operations which occur
   within the IMP-HOST interface.  The logic names appearing in the
   blocks correspond to the logic elements found in Appendix B.

Wingfield                                                       [Page 1]
RFC 12              IMP-HOST INTERFACE FLOW DIAGRAMS      26 August 1969

IMP to HOST Message
                       +----------+
                       |  Start   |
                       |  Input   |
                       +----------+
                             |
                             V
                 +------------------------+
                 | LAST <--0; IMPERR <--0 |
                 | PAD <--0; IN REQST <--0|
                 |  COUNTER <--0          |
                 +------------------------+      +---+
                             |<----------------- | B |
                             V                   +---+
                      +--------------+
                      | RFNIB <-- 1  |
                      +--------------+
                             |<--------------+
                             V               |
                            / \              |
                          /     \            |
                        / THERE'S \ N        |
                        \YOUR BIT /----------+
                          \=1 ? /
                            \ /
                             |
        +------------------->V
        |                   / \
   +----+------+    N     /     \
   | IMP ERROR |<------ /   IMP   \
   | <--- 1    |        \  READY  /
   +-----------+          \ ?   /
                            \ /
                             | Y
                             V
                            / \
                          /     \
   +-----------+   Y    /  LAST   \
   | PAD <-- 1 |<-------\ IMP BIT /
   +-----------+          \ =1? /
        |                   \ /                 +---+
        +------------------->|<-----------------| C |
                             V                  +---+
                +-----------------------+
                |    PULSE SHIFT REG.   |       +---+
                |   INCREMENT COUNTER   |------>| A |
                |      RFNTR <-- 0      |       +---+
                +-----------------------+

Wingfield                                                       [Page 2]
RFC 12              IMP-HOST INTERFACE FLOW DIAGRAMS      26 August 1969

      +---+                +---+
      | C |                | A |
      +-+-+                +-+-+
        ^                    |
        | Y                  V
       / \                  / \
     /     \          N   /WORD \
   /  PAD=1  \ <--------/ LENGTH  \
   \    ?    /          \   =1    /
     \     /              \  ?  /
       \ /                  \ /
        | N                  |
        V                    V
      +---+       +----------------------+
      | B |       |     INREQST <--1     |
      +---+       +----------------------+
                             |<-----------+
                             V            |
                            / \           |
                          /DATA \         |
                        /HAS BEEN \_N_____|
                        \ TAKEN   /
                          \ ?   /
                            \ /
                             V Y
                  +----------------------+
                  |    INREQST <--0      |
                  +----------------------+
                             V
                            / \
                          /     \              +------------+
                        / LAST = 1\----------->|   END  OF  |
                        \    ?    /            |   MESSAGE  |
                          \     /              +------------+
                            \ /                       ^
                             | N                      |
                             V                        |
                            / \                       |
                          /     \                     |
                        / PAD = 1 \-------------------+
                        \     ?   /
                          \     /
                            \ /
                             | N
                             V
   +---+          +---------------------+
   | B |<---------|    CLEAR COUNTER    |
   +---+          +---------------------+

Wingfield                                                       [Page 3]
RFC 12              IMP-HOST INTERFACE FLOW DIAGRAMS      26 August 1969

HOST TO IMP MESSAGE

            +--------------+
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