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MAX7301AAI+ Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX7301AAI+ Datasheet(HTML) 8 Page - Maxim Integrated Products |
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8 / 17 page  Initial Power-Up On initial power-up, all control registers are reset, and the MAX7301 enters shutdown mode (Table 4). Transition (Port Data Change) Detection Port transition detection allows any combination of the seven ports P24–P30 to be continuously monitored for changes in their logic status (Figure 5). A detected change is flagged on port P31, which is used as an active-high interrupt output (INT). Note that the MAX7301 does not identify which specific port(s) caused the inter- rupt, but provides an alert that one or more port levels have changed. The mask register contains 7 mask bits that select which of the seven ports, P24–P30 are to be monitored (Table 8). Set the appropriate mask bit to enable that port for transition detect. Clear the mask bit if transi- tions on that port are to be ignored. Transition detection works regardless of whether the port being monitored is set to input or output, but generally it is not particularly useful to enable transition detection for outputs. Port P31 must be configured as an output in order to work as the interrupt output INT when transition detec- tion is used. Port P31 is set as output by writing bit D7 = 0 and bit D6 = 1 to the port configuration register (Table 1). To use transition detection, first set up the mask regis- ter and configure port P31 as an output, as described above. Then enable transition detection by setting the M bit in the configuration register (Table 7). Whenever the configuration register is written with the M bit set, the MAX7301 updates an internal 7-bit snapshot register, which holds the comparison copy of the logic states of ports P24 through P30. The update action occurs regard- less of the previous state of the M bit, so that it is not nec- essary to clear the M bit and then set it again to update the snapshot register. When the configuration register is written with the M bit set, transition detection is enabled and remains enabled until either the configuration register is written with the M bit clear, or a transition is detected. The INT output port P31 goes low, if it was not already low. Once transition detection is enabled, the MAX7301 continuously compares the snapshot register against the changing states of P24 through P31. If a change on any of the monitored ports is detected, even for a short time (like a pulse), INT output port P31 is latched high. The INT output is not cleared if more changes occur or if the data pattern returns to its original snapshot con- dition. The only way to clear INT is to access (read or write) the transition detection mask register (Table 8). Transition detection is a one-shot event. When INT has been cleared after responding to a transition event, transition detection is automatically disabled, even though the M bit in the configuration register remains set (unless cleared by the user). Reenable transition detection by writing the configuration register with the M bit set, to take a new snapshot of the seven ports P24 to P30. Figure 2. 4-Wire Interface tCSH tCL tCSS tCH tCSH CS SCLK DIN DOUT tDS tDH tDO www.maximintegrated.com Maxim Integrated │ 8 MAX7301 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port I/O Expander |
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