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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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MPC5554 датащи(PDF) 11 Page - Freescale Semiconductor, Inc |
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MPC5554 датащи(HTML) 11 Page - Freescale Semiconductor, Inc |
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11 / 58 page  Electrical Characteristics MPC5554 Microcontroller Data Sheet, Rev. 4 Freescale Semiconductor 11 Furthermore, when all of the PORs negate, the system clock starts to toggle, adding another large increase of the current consumed by VRC33. If VRC33 lags VDDSYN by more than 100 mV, the increase in current consumed can drop VDD low enough to assert the 1.5 V POR again. Oscillations are possible when the 1.5 V POR asserts and stops the system clock, causing the voltage on VDD to rise until the 1.5 V POR negates again. All oscillations stop when VRC33 is powered sufficiently. When powering down, VRC33 and VDDSYN have no delta requirement to each other, because the bypass capacitors internal and external to the device are already charged. When not powering up or down, no delta between VRC33 and VDDSYN is required for the VRC to operate within specification. There are no power up/down sequencing requirements to prevent issues such as latch-up, excessive current spikes, and so on. Therefore, the state of the I/O pins during power up and power down varies depending on which supplies are powered. Table 7 gives the pin state for the sequence cases for all pins with pad type pad_fc (fast type). Table 8 gives the pin state for the sequence cases for all pins with pad type pad_mh (medium type) and pad_sh (slow type). The values in Table 7 and Table 8 do not include the effect of the weak-pull devices on the output pins during power up. Before exiting the internal POR state, the voltage on the pins go to a high-impedance state until POR negates. When the internal POR negates, the functional state of the signal during reset applies and the weak-pull devices (up or down) are enabled as defined in the device reference manual. If VDD is too low to correctly propagate the logic signals, the weak-pull devices can pull the signals to VDDE and VDDEH. Table 7. Pin Status for Fast Pads During the Power Sequence VDDE VDD33 VDD POR Pin Status for Fast Pad Output Driver pad_fc (fast) Low — — Asserted Low VDDE Low Low Asserted High VDDE Low VDD Asserted High VDDE VDD33 Low Asserted High impedance (Hi-Z) VDDE VDD33 VDD Asserted Hi-Z VDDE VDD33 VDD Negated Functional Table 8. Pin Status for Medium and Slow Pads During the Power Sequence VDDEH VDD POR Pin Status for Medium and Slow Pad Output Driver pad_mh (medium) pad_sh (slow) Low — Asserted Low VDDEH Low Asserted High impedance (Hi-Z) VDDEH VDD Asserted Hi-Z VDDEH VDD Negated Functional |
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