| 摘要 |
PROBLEM TO BE SOLVED: To reduce a circuit scale by providing an up/down counter which is up/down-controlled by the lowest bits of a reading address and a writing address as a means detecting a distance difference between the reading address and the writing address. SOLUTION: An up/down counter 15 inputs the lowest bit 221 of a writing address 112 as a count-up instruction signal, inputs the lowest bit 211 of a reading address 21 as a count down instruction signal and outputs the distance of both addresses as a counter output value. When a distance detection part 16 detects that the counter output value of the up/down counter 15 reaches a minimum regulated value or maximum regulated value which is previously decided, it judges an error state, transmits an initializing signal 23 and makes a reading address generation circuit 11 and a writing address generation circuit 12 return to an initial state. The distance detection part 16 transmits an alarm signal 24. |
