IBM 3270 ANR coax protocol.

[Henk Stegeman]

Hi,

Can anyone help me with detailed information of the IBM ANR coax protocol
used
between IBM 3271/72 and IBM 3277 terminals ?
'ANR' stands for Alpha Numeric Replacement.

This is what I know sofar of the ANR protocol:
- transmission was done with words of 13 bits.
- one bit time was 7 x 210nS = 1.47 uS (Not sure about the 7 x)
- a logical ZERO was defined as an negative pulse of  210 nS.
  a logical  ONE was defined as an  negative pulse of  630 nS. (3 x 210 nS)
- the 13 bits where used as follows:
  bit 1 - start bit (Busy bit)
  bit 2,3,4 - control bits
  bit 5 - 11 data bits
  bit 12 - odd parity over bits 2-11
  bit 13 - buffer size (480 / 1920 bits)

Transmission started with a dummy word with all 13 bits zero.
I assume this was needed to establish word synchronisation.
Followed by a WRITE CW1 and 480/1920 words.
The 480/1920 words can be of any mix of attribute / data words.

Currently I am building an async RS232 to ANR convertor and having
difficulties in
transfering data to an original IBM 3277 model 1 terminal.
The problem is most likely timing.

Does any one have an answer on the following question:
Q1:  the exact bit time ?
Q2:  exact pulse duration of logical ZERO and ONE ?
Q3:  time between words (if any).
Q4:  how was serial synchronisation maintained ?

Any piece of information of this ANR protocol is welcome.

Thanks !

Henk