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rfc:rfc12

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

          +--------------+
          | START OUTPUT |
          +------+-------+
                 V
     +------------------------+
     | COUNTER <-- 1          |
     | LSTWD <--0; BTAVL <--0 |
     +-----------+------------+        +---+
                 |<--------------------| C |
                 V                     +---+
     +-----------+------------+
     |    OUT REQST <-- 1     |
     |     CLEAR SHIFT REG.   |
     +-----------+------------+
   +------------>|
   |             V
   |            / \
   |      N   /     \
   |_______ / STROBE  \
            \DATA WORD/
              \ =1 ?/
                \ /
                 V  Y
    +------------+------------+
    |  LOAD SHIFT  REGISTER   |
    |  OUTREQST <-- 0         |
    |  COUNTER  <-- 1         |
    +-------------------------+
    +---------->|
    |           V
    |          / \
    |        /     \
    |N     / RFNBIT  \
    +----- \   = 1   /
             \   ? /            +----------+
               \ /              |          | N
                V   Y           |         / \
       +--------+--------+      V       /     \
       |  THERE'S YOUR   |----------->/ RFNBIT  \
       | HOST BET <-- 1  |            \  = 0    /
       +-----------------+              \  ?  /
                                          \ /
                                           | Y
                                         +-+-+
                                         | A |
                                         +---+

Wingfield [Page 4] RFC 12 IMP-HOST INTERFACE FLOW DIAGRAMS 26 August 1969

                             +---+
                             | A |
                             +---+
                               V
                +--------------+-------------+
                | THERE'S YOUR HOST BIT <--0 |
                |      BTAVL <-- 0           |
                +----------------------------+
                               V
                              / \                   / \
                            / WORD\   Y           /     \   Y
                          /LENGTH -1\---------->/  LSTWD  \---+
                          \   = 1   /           \   = 1   /   |
                            \  ?  /               \  ?  /     |
                              \ /                   \ /       |
                               | N                   | N      |
                               V                     |        |
                              / \                    |        |
                            / WORD\                  |        V
         ________________ / LENGTH  \                |  +------------+
         |                \  = 1    /                |  | LIBIT <- 1 |
         |                  \  ?  /                  |  +------------+
         |                    \ /                    V        |
         |                     |<-----------------------<------+
         |                     V
         |            +-----------------+
         |            | PUSH SHIFT REG. |
  +-------------+     |INCREMENT COUNTER|
  | LIBIT <-- 0 |     +-----------------+
  +-------------+              V
         |                   +---+
         |                   | B |
         V                   +---+
        / \
      /     \
    /  LSTWD  \ Y                          +-------------+
    \   = 1   /--------------------------->|   END OF    |
      \  ?  /                              |   MESSAGE   |
        \ /                                +-------------+
         | N
         V
       +---+
       | C |
       +---+
       [ This RFC was put into machine readable form for entry ]
           [ into the online RFC archives by Lorrie Shiota]

Wingfield [Page 5] RFC 12 IMP-HOST INTERFACE FLOW DIAGRAMS 26 August 1969

Wingfield [Page 6]

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