Bit rate matching system and method
View Patent ↗This relates to a method for determining a receive bit rate over a data link. The method includes setting a receive bit rate to an initial bit rate. A bit pattern over the data link is detected using the initial bit rate. A determination is made as to whether the detected bit pattern matches one of a plurality of known bit patterns corresponding to fractional bit rates. If the detected bit pattern does not match one of the plurality of known bit patterns, then a determination is made as to whether the received data includes a framing error. If it does, then the receive bit rate is lowered to a low detection bit rate that is lower than the fractional bit rates corresponding to the plurality of known bit patterns.
1. A method for determining a receive bit rate over a data link, comprising:
setting a receive bit rate to an initial bit rate;
detecting a bit pattern over the data link using the initial bit rate, wherein the detected bit pattern includes a start bit;
determining if the detected bit pattern matches one of a plurality of known bit patterns corresponding to fractional bit rates; and
if the detected bit pattern does not match one of said plurality of known bit patterns corresponding to fractional bit rates, then determining if the received data includes a framing error, wherein the framing error is due to the pattern not changing state during a predetermined time period, and if so then lowering the receive bit rate to a low detection bit rate that is lower than the fractional bit rates corresponding to the plurality of known bit patterns, and
after said lowering of the receive bit rate receiving a confirmation bit pattern over the data link within a predetermined time period:
if the confirmation bit pattern is correctly received, then setting the receive bit rate, for detecting subsequent data over the data link, to the low bit rate;
if the confirmation bit pattern is not correctly received, then resetting the receive bit rate, for the detecting subsequent data over the data link, to the initial bit rate, and
if the confirmation bit pattern is not over the data link within the predetermined time period, then resetting the receive bit rate, for detecting subsequent data over the data link, to the initial bit rate.
2. The method of claim 1 wherein the initial bit rate is a highest supported bit rate.
3. The method of claim 1 wherein the low detection bit rate is one ninth of the initial bit rate.
4. The method of claim 1 further comprising:
determining if the detected bit pattern matches an expected bit pattern corresponding to data transmitted at the initial bit rate; and
if not, then performing the determining step of determining if the detected bit pattern matches one of the plurality of known bit patterns corresponding to fractional bit rates.
5. The method of claim 4 , wherein the expected bit pattern is a data byte having a value of OxFF.
6. The method of claim 1 , wherein the plurality of known bit patterns includes data bytes having values of OxFE, OxFC and OxEO.
7. The method of claim 1 wherein the part of the pattern that has not changed state during the predetermined time period is the start bit.
8. The method of claim 1 wherein the fractional bit rates include one half, one third and one fourth the initial bit rate.
9. The method of claim 1 wherein the detecting step and the determining steps are performed by a modem.