MMPI - This is done to initiailze the period for the company codes not for regular use. This will open your previous period which u have closed. T.code MMPI is used to open the old period in which you want to post. It is used for the first time when you start period after factory calendor settings.
MMPV - This will open your next period. It is done to close the current period and open the new period. If we enter the date or month in MMPV means we are opening that date or month by closing previous date or month. Never use MMPV without completing the transaction in previous month.For e.g. we have to open the JAN then for the given company we can close the DEC. In this way we can post our postiong in JAN month.
MMRV - To Check the Current Period in company and to allow postings in previous periods. It is done when you have to display and view the prevoius period and current period. It is used to allow posting in a previous period as per your company requirement.
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