SLAU144K December 2004 – August 2022 MSP430AFE221 , MSP430AFE222 , MSP430AFE223 , MSP430AFE231 , MSP430AFE232 , MSP430AFE233 , MSP430AFE251 , MSP430AFE252 , MSP430AFE253 , MSP430F2001 , MSP430F2002 , MSP430F2003 , MSP430F2011 , MSP430F2012 , MSP430F2013 , MSP430F2101 , MSP430F2111 , MSP430F2112 , MSP430F2121 , MSP430F2122 , MSP430F2131 , MSP430F2132 , MSP430F2132-EP , MSP430F2232 , MSP430F2234 , MSP430F2252 , MSP430F2252-Q1 , MSP430F2254 , MSP430F2272 , MSP430F2272-Q1 , MSP430F2274 , MSP430F2274-EP , MSP430F233 , MSP430F2330 , MSP430F235 , MSP430F2350 , MSP430F2370 , MSP430F2410 , MSP430F2416 , MSP430F2417 , MSP430F2418 , MSP430F2419 , MSP430F247 , MSP430F2471 , MSP430F248 , MSP430F2481 , MSP430F249 , MSP430F2491 , MSP430F2616 , MSP430F2617 , MSP430F2618 , MSP430F2619 , MSP430G2001 , MSP430G2101 , MSP430G2102 , MSP430G2111 , MSP430G2112 , MSP430G2121 , MSP430G2131 , MSP430G2132 , MSP430G2152 , MSP430G2153 , MSP430G2201 , MSP430G2201-Q1 , MSP430G2202 , MSP430G2203 , MSP430G2210 , MSP430G2211 , MSP430G2212 , MSP430G2213 , MSP430G2221 , MSP430G2230 , MSP430G2231 , MSP430G2231-Q1 , MSP430G2232 , MSP430G2233 , MSP430G2252 , MSP430G2253 , MSP430G2302 , MSP430G2303 , MSP430G2312 , MSP430G2313 , MSP430G2332 , MSP430G2333 , MSP430G2352 , MSP430G2353 , MSP430G2402 , MSP430G2403 , MSP430G2412 , MSP430G2413 , MSP430G2432 , MSP430G2433 , MSP430G2444 , MSP430G2452 , MSP430G2453 , MSP430G2513 , MSP430G2533 , MSP430G2544 , MSP430G2553 , MSP430G2744 , MSP430G2755 , MSP430G2855 , MSP430G2955 , MSP430TCH5E
When multiple channels are grouped the SD24PREx registers can be used to delay the conversion time frame for each channel. Using SD24PREx, the decimation time of the digital filter is increased by the specified number of fM clock cycles and can range from 0 to 255. Figure 27-9 shows an example using SD24PREx.
The SD24PREx delay is applied to the beginning of the next conversion cycle after being written. The delay is used on the first conversion after SD24SC is set and on the conversion cycle following each write to SD24PREx. Following conversions are not delayed. After modifying SD24PREx, the next write to SD24PREx should not occur until the next conversion cycle is completed, otherwise the conversion results may be incorrect.
The accuracy of the result for the delayed conversion cycle using SD24PREx is dependent on the length of the delay and the frequency of the analog signal being sampled. For example, when measuring a DC signal, SD24PREx delay has no effect on the conversion result regardless of the duration. The user must determine when the delayed conversion result is useful in their application.
Figure 27-10 shows the operation of grouped channels 0 and 1. The preload register of channel 1 is loaded with zero resulting in immediate conversion whereas the conversion cycle of channel 0 is delayed by setting SD24PRE0 = 8. The first channel 0 conversion uses SD24PREx = 8, shifting all subsequent conversions by eight fM clock cycles.
When channels are grouped, care must be taken when a channel or channels operate in single conversion mode or are disabled in software while the master channel remains active. Each time channels in the group are re-enabled and re-synchronize with the master channel, the preload delay for that channel will be reintroduced. Figure 27-11 shows the re-synchronization and preload delays for channels in a group. It is recommended that SD24PREx = 0 for the master channel to maintain a consistent delay between the master and remaining channels in the group when they are re-enabled.