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CAT522LI Datasheet(PDF) 8 Page - Catalyst Semiconductor |
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CAT522LI Datasheet(HTML) 8 Page - Catalyst Semiconductor |
8 / 15 page CAT522 Doc. No. MD-2004 Rev. G 8 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice READING DATA Each time data is transferred into a DPP control register currently held data is shifted out via the D0 pin, thus in every data transaction a read cycle occurs. Note, however, that the reading process is destructive. Data must be removed from the register in order to be read. Figure 2 depicts a Read Only cycle in which no change occurs in the DPP’s output. This feature allows µPs to poll DPPs for their current setting without disturbing the output voltage but it assumes that the setting being read is also stored in non-volatile memory so that it can be restored at the end of the read cycle. In Figure 2 CS returns low before the 13th clock cycle completes. In doing so the non-volatile memory setting is reloaded into the DPP wiper control register. Since this value is the same as that which had been there previously no change in the DPP’s output is noticed. Had the value held in the control register been different from that stored in non- volatile memory then a change would occur at the read cycle’s conclusion. TEMPORARILY CHANGE OUTPUT The CAT522 allows temporary changes in DPP’s output to be made without disturbing the settings retained in non-volatile memory. This feature is parti– cularly useful when testing for a new output setting and allows for user adjustment of preset or default values without losing the original factory settings. Figure 3 shows the control and data signals needed to effect a temporary output change. DPP wiper settings may be changed as many times as required and can be made to any of the two DPPs in any order or sequence. The temporary setting(s) remain in effect long as CS remains high. When CS returns low all two DPPs will return to the output values stored in non-volatile memory. When it is desired to save a new setting acquired using this feature, the new value must be reloaded into the DPP wiper control register prior to programming. This is because the CAT522’s internal control circuitry discards from the programming register the new data two clock cycles after receiving it if no PROG signal is received. Figure 2. Reading from Memory Figure 3. Temporary Change in Output A0 A1 1 DO DI CS PROG DPP OUTPUT t 1 2 3 4 5 6 7 8 9 10 11 12 o CURRENT DPP VALUE NON-VOL ATILE D0 D1 D2 D3 D4 D5 D6 D7 CURRENT DPP DATA RDY/BSY D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 D0 D1 D2 D3 D4 D5 D6 D7 1 NEW DPP DATA CURRENT DPP DATA DO DI CS PROG DPP OUTPUT t 1 2 3 4 5 6 7 8 9 10 11 12 N N+1 N+2 o CURRENT DPP VALUE NON-VOL ATILE NEW DPP VALUE VOLATILE CURRENT DPP VALUE NON-VOL ATILE RDY/BSY |
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