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