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71M6534 Datasheet(PDF) 72 Page - Maxim Integrated Products |
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71M6534 Datasheet(HTML) 72 Page - Maxim Integrated Products |
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72 / 132 page  71M6533/G/H and 71M6534/H Data Sheet FDS_6533_6534_004 72 Rev 2 4.1.2 System Temperature Compensation In a production electricity meter, the 71M6533 and 71M6534 is not the only component contributing to temperature dependency. A whole range of components (e.g. current transformers, resistor dividers, power sources, filter capacitors) will contribute temperature effects. Since the output of the on-chip temperature sensor is accessible to the MPU, temperature compensation mechanisms with great flexibility are possible. MPU access to GAIN_ADJ permits a system-wide temperature correction over the entire meter rather than local to the chip. 4.1.3 Temperature Compensation for the RTC In order to obtain accurate readings from the RTC, the following calibration procedures are recommended: 1. At the time of meter calibration, the crystal oscillator may be calibrated using the RTCA_ADJ register in I/O RAM to be as close to 32768 Hz as possible. The recommended procedure is to connect a high- precision frequency counter to the TMUXOUT pin and select 0x11 for TMUX[4:0]. This will generate a 4-second pulse at TMUXOUT that can be used to trim RTCA_ADJ to the best value. A wider trim range is achieved with the I/O RAM registers PREG[16:0] and QREG[1:0]. 2. When the meter is in service, the MPU takes frequent temperature readings. If the temperature characteristics of the crystal are known, the temperature readings can be used to modify the settings for the I/O RAM registers PREG[16:0] and QREG[1:0] in order to keep the crystal frequency close to 32768 Hz. 3. After periods of operation under battery power, the temperature for the time the meter was not powered can be estimated by averaging the temperatures before and after battery operation. Based on this, the overall correction for the RTC time can be calculated and applied to the RTC after main power returns to the meter. 4.2 Connecting LCDs The 71M6533 and 71M6534 have an on-chip LCD controller capable of controlling static or multiplexed LCDs. Figure 36 shows the basic connection for an LCD. The following dedicated and multi-use pins can be assigned as LCD segments: • 15 dedicated LCD segment pins: SEG0 to SEG2, SEG8, SEG12 to SEG18, SEG20 to SEG23. • 9 dual-function pins: MUX_SYNC/SEG7, CKTEST/SEG19, E_RXTX/SEG9, E_TCLK/SEG10, E_RST/SEG11, SEG3/PCLK, SEG4/PSDO, SEG5/PCSZ, SEG6/PSDI. • 5 additional dual-function pins in the 71M6534: SEG51/E_TBUS0, SEG52/E_TBUS1, SEG53/E_TBUS2, SEG54/E_TBUS3, SEG55/E_ISYNC • 33 (71M6533) or 46 (71M6534) combined DIO and segment pins o 71M6533: SEG24/DIO4 to SEG31/DIO11, SEG33/DIO13 to SEG41/DIO21, SEG43/DIO23 to SEG47/DIO27, SEG49/DIO29, SEG50/DIO30, SEG61/DIO41, SEG63/DIO43 to SEG65/DIO45, and SEG67/DIO47 to SEG71/DIO51. o 71M6534: SEG24/DIO4 to SEG50/DIO30, SEG56/DIO36 to SEG59/DIO39, SEG61/DIO41 to SEG75/DIO55. |
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