Part # Application Note General Purpose Products Accessories Audio Body Electronic Body And Convenience Car Entertainment Car Networks datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: Correct Power-On and Power-Off for the M93Cxx and M93Sxx


Part Details:

AN1119 APPLICATION NOTE Correct Power-On and Power-Off for the M93Cxx and M93Sxx This document has been written for those users who have become used to using the members of theST93C/CSxx and M93C/Sxx family outside of their specifications. Table 1. Members of the ST93C/CSxx and M93Cxx Family Earlier Members Later members ST93C06 M93C06 ST93C46, ST93CS46 M93C46, M93S46 ST93C56, ST93CS56 M93C56, M93S56 ST93C66, ST93CS66 M93C66, M93S66 M93C86, M93S86 It is very important to use each of these devices only in the way specified in the data sheets. In particular,as shown in Figure 1, it is important for the Serial Clock (C) input to be held Low whenever there is a risingedge on the Chip Select (S) input. Figure 1. Correct Sequence S C Held at 0 Ai02463 October 2001 1/6 AN1119 - APPLICATION NOTE If a rising edge of the Chip Select (S) input is allowed to occur while the Serial Clock (C) input is High orhigh-impedance, as shown in Figure 2, the behavior of the device becomes unpredictable. Figure 2. Hazardous Sequence S C High-Z or 1 Ai02462B MAIN SOURCES OF ERROR: POWER-UP AND MCU RECOVERY START-UPThere are two main causes of users using these devices outside their specifications: s Uncontrolled inputs during Power-Up and Power-Down s Uncontrolled inputs during Microcontroller Recovery Start-up Time Uncontrolled Inputs During Power-Up and Power-DownDuring power-up, all three input lines (C, D and S) start in their uncharged state, and might well be undriv-en. There is no control of Low-to-High transitions being picked up from noise. Also, there is no guaranteethat if drive is later applied simultaneously to the three signals, that the Chip Select (S) line will cross theLow-to-High threshold before either of the other two. During power-down, the problem of noise pick-up on undriven lines returns as the main source of hazard. Most microcontrollers will attempt to avoid these problems by going into a Microcontroller Recovery Start-up Mode when the VCC line is outside its specified range. However, as discussed next, this does not com-pletely resolve the problems. Uncontrolled Inputs During Microcontroller Recovery Start-up TimeDuring the Microcontroller Recovery Start-up Time, which is typically several milliseconds in duration,some microcontrollers configure all I/O lines in their input mode, as shown in Figure 3. That is, they are allset to their high-impedance state. Under these conditions, with inputs C, D and S all undriven, each linebehaves like a small antenna, and can pick up electromagnetic noise radiation. It is not impossible forthere to be a rising edge on the Chip Select (S) input while C or D is floating High. Alternatively, some microcontrollers configure all I/O lines as outputs during the Microcontroller RecoveryStart-up Time, and drive the lines High. As soon as Chip Select (S) crosses the Low-to-High threshold,the EEPROM is enabled, and will decode whatever enters its D and C inputs. If these are acting outsidethe specification, the behavior of the EEPROM becomes unpredictable. 2/6 AN1119 - APPLICATION NOTE Figure 3. All Signals Being Treated as Inputs input Q (data-output) input D Microcontroller M93xxx (MCU) EEPROM


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