| 摘要 |
PURPOSE:To attain a high-quality O-order group transmission line for digital data communication network by substituting a status bit with a status bit of the same channel one frame before if error of a frame pattern is detected when a frame synchronizing circuit is in the synchronous state. CONSTITUTION:If the input frame pattern is erroneous in the synchronous state, a protecting circuit 4-d judges to be an out of frame synchronism to set a means 4-7 to ''1'' when a ratio of error to correct as the result of comparison of a means 4-j reaches a certain threshold. A status bit 4-6 is inputted to a separating circuit 4-n selected by a selector 4-g as it is when the frame synchronizing circuit is in the true synchronous state. However, if the frame pattern is erroneous in the synchronous state, the status bit of the same channel one frame before which is delayed by a means 4-f is selected by the selector 4-g in accordance with a signal of a means 4-12 and is inputted to a separating circuit 4-h, and thus, the status bit is protected. |
