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LM628 Datasheet(PDF) 14 Page - National Semiconductor (TI) |
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LM628 Datasheet(HTML) 14 Page - National Semiconductor (TI) |
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14 / 24 page  Interrupt Control Commands (Continued) TABLE 3. Mask and Reset Bit Allocations for Interrupts Bit Position Function Bits 15 thru 7 Not Used Bit 6 Breakpoint Interrupt Bit 5 Position-Error Interrupt Bit 4 Wrap-Around Interrupt Bit 3 Index-Pulse Interrupt Bit 2 Trajectory-Complete Interrupt Bit 1 Command-Error Interrupt Bit 0 Not Used RSTI COMMAND: ReSeT Interrupts Command Code: 1D Hex Data Bytes: Two Data Range: See Text Executable During Motion: Yes When one of the potential interrupt conditions of Table 3 oc- curs, command RSTI is used to reset the corresponding in- terrupt flag bit in the status byte. The host may reset one or all flag bits. Resetting them one at a time allows the host to service them one at a time according to a priority pro- grammed by the user. As in the MSKI command, bits 1 through 6 of the second (less significant) byte correspond to the potential interrupt conditions shown in Table 3. Also see description of RDSTAT command. Any zero(s) in this 6-bit field reset the corresponding interrupt(s). The remaining bits have no effect. Filter Control Commands The following two LM628 user commands are used for set- ting the derivative-term sampling interval, for adjusting the filter parameters as required to tune the system, and to con- trol the timing of these system changes. LFIL COMMAND: Load FILter Parameters Command Code: 1E Hex Data Bytes: Two to Ten Data Ranges… Filter Control Word: See Text Filter Coefficients: 0000 to 7FFF Hex (Pos Only) Integration Limit: 0000 to 7FFF Hex (Pos Only) Executable During Motion: Yes The filter parameters (coefficients) which are written to the LM628 to control loop compensation are: kp, ki, kd, and il (in- tegration limit). The integration limit (il) constrains the contri- bution of the integration term (see Eq. 1) to values equal to or less than a user-defined maximum value; this capability minimizes integral or reset “wind-up” (an overshooting effect of the integral action). The positive-only input value is compared to the absolute magni- tude of the integration term; when the magnitude of integra- tion term value exceeds il, the il value (with appropriate sign) is substituted for the integration term value. The derivative-term sampling interval is also programmable via this command. After writing the command code, the first two data bytes that are written specify the derivative-term sampling interval and which of the four filter parameters is/ are to be written via any forthcoming data bytes. The first byte written is the more significant. Thus the two data bytes constitute a filter control word that informs the LM628 as to the nature and number of any following data bytes. See Table 4. TABLE 4. Filter Control word Bit Allocation Bit Position Function Bit 15 Derivative Sampling Interval Bit 7 Bit 14 Derivative Sampling Interval Bit 6 Bit 13 Derivative Sampling Interval Bit 5 Bit 12 Derivative Sampling Interval Bit 4 Bit 11 Derivative Sampling Interval Bit 3 Bit 10 Derivative Sampling Interval Bit 2 Bit 9 Derivative Sampling Interval Bit 1 Bit 8 Derivative Sampling Interval Bit 0 Bit 7 Not Used Bit 6 Not Used Bit 5 Not Used Bit 4 Not Used Bit 3 Loading kp Data Bit 2 Loading ki Data Bit 1 Loading kd Data Bit 0 Loading il Data Bits 8 through 15 select the derivative-term sampling inter- val. See Table 5. The user must locally save and restore these bits during successive writes of the filter control word. Bits 4 through 7 of the filter control word are not used. Bits 0 to 3 inform the LM628 as to whether any or all of the filter parameters are about to be written. The user may choose to update any or all (or none) of the filter parameters. Those chosen for updating are so indicated by logic one(s) in the corresponding bit position(s) of the filter control word. The data bytes specified by and immediately following the fil- ter control word are written in pairs to comprise 16-bit words. The order of sending the data words to the LM628 corre- sponds to the descending order shown in the above descrip- tion of the filter control word; i.e., beginning with kp, then ki, kd and il. The first byte of each word is the more-significant byte. Prior to writing a word (byte pair) it is necessary to check the busy bit in the status byte for readiness. The re- quired data is written to the primary buffers of a double-buffered scheme by the above described operations; it is not transferred to the secondary (working) registers until the UDF command is executed. This fact can be used ad- vantageously; the user can input numerous data ahead of their actual use. This simple pipeline effect can relieve po- tential host computer data communications bottlenecks, and facilitates easier synchronization of multiple-axis controls. UDF COMMAND: UpDate Filter Command Code: 04 Hex Data Bytes: None www.national.com 14 |
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