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HC6856WSHAC35 Datasheet(PDF) 8 Page - Honeywell Solid State Electronics Center |
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HC6856WSHAC35 Datasheet(HTML) 8 Page - Honeywell Solid State Electronics Center |
8 / 12 page HC6856 8 Read Cycle The RAM is asynchronous in operation, allowing the read cycle to be controlled by address, chip select (NCS), or chip enable (CE) (refer to Read Cycle timing diagram). To perform a valid read operation, both chip select and output enable (NOE) must be low and chip enable and write enable (NWE) must be high. The output drivers can be controlled independently by the NOE signal. Consecutive read cycles can be executed with NCS held continuously low, and with CE held continuously high. For an address activated read cycle, NCS and CE must be valid prior to or coincident with the activating address edge transition(s). Any amount of toggling or skew between address edge transitions is permissible; however, data outputs will become valid TAVQV time following the latest occurring address edge transition. The minimum address activated read cycle time is TAVAV. When the RAM is operated at the minimum address activated read cycle time, the data outputs will remain valid on the RAM I/O until TAXQX time following the next sequential address transi- tion. To control a read cycle with NCS, all addresses and CE must be valid prior to or coincident with the enabling NCS edge transition. Address or CE edge transitions can occur later than the specified setup times to NCS; however, the valid data access time will be delayed. Any address edge transition, which occurs during the time when NCS is low, will initiate a new read access, and data outputs will not become valid until TAVQV time following the address edge transition. Data outputs will enter a high impedance state TSHQZ time following a disabling NCS edge transition. To control a read cycle with CE, all addresses and NCS must be valid prior to or coincident with the enabling CE edge transition. Address or NCS edge transitions can occur later than the specified setup times to CE; however, the valid data access time will be delayed. Any address edge transition which occurs during the time when CE is high will initiate a new read access, and data outputs will not become valid until TAVQV time following the address edge transition. Data outputs will enter a high impedance state TELQZ time following a disabling CE edge transition. DYNAMIC ELECTRICAL CHARACTERISTICS Write Cycle The write operation is synchronous with respect to the address bits, and control is governed by write enable (NWE), chip select (NCS), or chip enable (CE) edge transitions (refer to Write Cycle timing diagrams). To per- form a write operation, both NWE and NCS must be low, and CE must be high. Consecutive write cycles can be performed with NWE or NCS held continuously low, or CE held continuously high. At least one of the control signals must transition to the opposite state between consecutive write operations. The write mode can be controlled via three different control signals: NWE, NCS, and CE. All three modes of control are similar except the NCS and CE controlled modes actually disable the RAM during the write recovery pulse. Only the NWE controlled mode is shown in the table and diagram on the previous page for simplicity; however, each mode of control provides the same write cycle timing characteris- tics. Thus, some of the parameter names referenced below are not shown in the write cycle table or diagram, but indicate which control pin is in control as it switches high or low. To write data into the RAM, NWE and NCS must be held low and CE must be held high for at least TWLWH/TSLSH/ TEHEL time. Any amount of edge skew between the signals can be tolerated, and any one of the control signals can initiate or terminate the write operation. For consecu- tive write operations, write pulses must be separated by the minimum specified TWHWL/TSHSL/TELEH time. Address inputs must be valid at least TAVWL/TAVSL/TAVEH time before the enabling NWE/NCS/CE edge transition, and must remain valid during the entire write time. A valid data overlap of write pulse width time of TDVWH/TDVSH/TDVEL, and an address valid to end of write time of TAVWH/ TAVSH/TAVEL also must be provided for during the write operation. Hold times for address inputs and data inputs with respect to the disabling NWE/NCS/CE edge transition must be a minimum of TWHAX/TSHAX/TELAX time and TWHDX/TSHDX/TELDX time, respectively. The minimum write cycle time is TAVAV. |
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