| 摘要 |
A tape drive system (11) for reading a magnetic tape (13) includes a drive mechanism 15, a read head (17), a servo controller (19), read and mark detect circuitry (21), a speed decoder (23), and novel position capture circuitry (25). The position capture circuitry includes a register (27) with addresses (31-34) each dedicated to storing a value for a predetermined type of position as a function of which input line (41-44) a detection or request is received. The position capture circuitry includes a input-polling state machine (101) to ensure each detection results in exactly one position value transfer. A timing section (103) synchronizes the polling of inputs with data transfers. A bus multiplexing section (105) provides for 12-bit resolution over 8-bit busses. The position types can be data block boundaries or reel-encoder marks or position requested by the servo controller. The input lines (41-44) are polled routinely, ensuring that the stored values precisely reflect the referenced positions.
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