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7M13: Difference between revisions
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==Internals and Repair Issues== | ==Internals and Repair Issues== | ||
The 7M13 is relatively simple and robust electrically | The 7M13 is relatively simple and robust electrically, consisting mostly of 74xx TTL logic. | ||
However, there can be electromechanical problems due to the number of switches. | |||
For example, a 7M13 may appear unresponsive if the | For example, a 7M13 may appear unresponsive if the "(P)RESET" button for the camera counter is not fully released. | ||
The 7M13 uses four 7489 TTL 16×4 RAMs to store the characters entered, | The 7M13 uses four 7489 TTL 16×4 RAMs to store the characters entered, | ||
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One RAM and D/A each are assigned to row and column readout signals in each channel, | One RAM and D/A each are assigned to row and column readout signals in each channel, | ||
and are addressed by a counter synchronized to the readout time slot pulses. | and are addressed by a counter synchronized to the readout time slot pulses. | ||
In other words, characters are not stored | In other words, characters are not stored as ASCII bytes, but as row/column pairs | ||
matching the [[Media:Tek7000-readout-charset.jpg|readout system's character set]]. | matching the [[Media:Tek7000-readout-charset.jpg|readout system's character set]]. | ||
The keyboard is arranged in a matching matrix of double-contact (DPST) keys | The keyboard is arranged in a matching matrix of double-contact (DPST) keys | ||