agillesp@Daisy.EE.UND.AC.ZA (Andrew M Gillespie) (03/19/91)
I have been wondering whether the transputer serial-link communication is
synchronous or asynchronous, and what mechanism is then used to receive
data. The "TRANSPUTER DATABOOK 2nd ed 1989" states that "Data reception is
asynchronous, allowing communication to be independent of clock phase".
Asynchronous systems function by scanning the incoming data line at up
to 64 * transmission clock rate (presumably 20 MHz for a 20 MBit/s link) to
determine the start of the data frame. It seems somewhat unlikely that this is
indeed the case as this would involve excessively high frequencies inside
the transputer (i.e. 320 MHz for 16* clock).
It seems obvious that if clocks conforming to a specified accuracy are
used in both transmitting and receiving transputers, and messages are kept
short (2 start + 8 data + 1 stop bits in this case), the small differences
in frequency will have negligible effect on the communication.
To compensate for phase differences between the Tx and Rx clocks, the receiver
has to detect the start of the transmission (synchronise with the Tx clock),
usually this is done as stated above, using a clock divided down from the
64* clock to receive the data. The uncertainty in this case is presumably
(1/64 * transmission clock period).
Synchronous systems extract a clock embedded in the data stream, and use this
to extract the data. This requires that the transmission frequency be twice
the data bit frequency. There is however no clock embedded in the transputer
link-data, so the communication is presumably not synchronous (?).
Does anyone out there know exactly how the transputer-link mechanism works,
and could describe both the mechanism and a circuit to implement such a
mechanism ?
Thanks
Andy
--
Andrew M Gillespie, Dept of Electrical Engineering, University of Natal,
King George V Ave, Durban, Republic of South Africa, 4001.
Fax: National: (031) 8162725 International: 27-31-8162725
email: Agillesp@Daisy.EE.UND.AC.ZA