| 摘要 |
<p>The keys of telephone toll service positions have contacts to supply a 3-out-of-9 code on a nine-wire bus. The scanner has multiplex circuits to interrogate the position busses sequentially. There are two bistable devices individual to each position, and two common bistable devices to remember the status from cycle to cycle so that a key must be closed for two cycles to generate a valid message, and another message is not generated until after the key is opened. For some keys an "indication on release" message is generated when the key is opened, under control of the bistable devices. There are seven buffer registers into which messages are loaded in sequence , and which are unloaded in sequence for transmission to a central processor. A key interpreter checks for three or more bits out of nine, all zeros, all ones indicating an unequipped position, or a code common to keys requiring indication or release.</p> |
