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IETF RFC 12
IMP-Host interface flow diagrams
Last modified on Friday, September 29th, 2006
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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
+--------------+
| 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
IMP-Host interface flow diagrams
RFC TOTAL SIZE: 9221 bytes
PUBLICATION DATE: Friday, September 29th, 2006
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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