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PC7447MG933L Datasheet(PDF) 56 Page - ATMEL Corporation |
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PC7447MG933L Datasheet(HTML) 56 Page - ATMEL Corporation |
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56 / 66 page  56 PC7457/47 [Preliminary] 5345B–HIREL–02/04 Pull-up/Pull-down Resistor Requirements The PC7457 requires high-resistive (weak: 4.7 k Ω) pull-up resistors on several control pins of the bus interface to maintain the control signals in the negated state after they have been actively negated and released by the PC7457 or other bus masters. These pins are TS, ARTRY, SHDO, and SHD1. Some pins designated as being for factory test must be pulled up to OVDD or down to GND to ensure proper device operation. For the PC7447, 360 BGA, the pins that must be pulled up to OVDD are LSSD_MODE and TEST[0:3]; the pins that must be pulled down to GND are L1_TSTCLK and TEST[4]. For the PC7457, 483 BGA, the pins that must be pulled up to OVDD are LSSD_MODE and TEST[0:5]; the pins that must be pulled down are L1_TSTCLK and TEST[6]. The CKSTP_IN signal should likewise be pulled up through a pull-up resistor (weak or stronger: 4.7 – 1 k Ω) to prevent erroneous assertions of this signal. In addition, the PC7457 has one open-drain style output that requires a pull-up resistor (weak or stronger: 4.7 – 1 k Ω) if it is used by the system. This pin is CKSTP_OUT. If pull-down resistors are used to configure BVSEL or L3VSEL, the resistors should be less than 250 Ω (see Table 16 on page 40). Because PLL_CFG[0:4] must remain stable during normal operation, strong pull-up and pull-down resistors (1 k Ω or less) are rec- ommended to configure these signals in order to protect against erroneous switching due to ground bounce, power supply noise or noise coupling. During inactive periods on the bus, the address and transfer attributes may not be driven by any master and may, therefore, float in the high-impedance state for relatively long periods of time. Because the PC7457 must continually monitor these signals for snooping, this float condition may cause excessive power draw by the input receivers on the PC7457 or by other receivers in the system. It is recommended that these signals be pulled up through weak (4.7 k Ω) pull-up resistors by the system, or that they may be oth- erwise driven by the system during inactive periods of the bus. The snooped address and transfer attribute inputs are A[0:35], AP[0:4], TT[0:4], CI, WT, and GBL. If extended addressing is not used, A[0:3] are unused and must be pulled low to GND through weak pull-down resistors. If the PC7457 is in 60x bus mode, DTI[0:3] must be pulled low to GND through weak pull-down resistors. The data bus input receivers are normally turned off when no read operation is in progress and, therefore, don’t require pull-up resistors on the bus. Other data bus receiv- ers in the system, however, may require pull-ups, or that those signals be otherwise driven by the system during inactive periods by the system. The data bus signals are D[0:63] and DP[0:7]. If address or data parity is not used by the system, and the respective parity checking is disabled through HID0, the input receivers for those pins are disabled, and those pins don’t require pull-up resistors and should be left unconnected by the system. If all parity generation is disabled through HID0, then all parity checking should also be disabled through HID0, and all parity pins may be left unconnected by the system. The L3 interface does not normally require pull-up resistors. |
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