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MCM69R820AZP7 Datasheet(PDF) 11 Page - Motorola, Inc |
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MCM69R820AZP7 Datasheet(HTML) 11 Page - Motorola, Inc |
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11 / 20 page  MCM69R738A •MCM69R820A 11 MOTOROLA FAST SRAM FUNCTIONAL OPERATION READ AND WRITE OPERATIONS All control signals except G are registered on the rising edge of the CK clock. These signals must meet the setup and hold times shown in the AC Characteristics table. On the rising edge of the following clock, read data is clocked into the output register and available at the outputs at tKHQV. Dur- ing this same cycle a new read address can be applied to the address pins. A deselect cycle (dead cycle) must occur prior to a write cycle. Read cycles may follow write cycles immediately. G, SS, and SW control output drive. Chip deselect via a high on SS at the rising edge of the CK clock has its effect on the output drivers after the next rising edge of the CK clock. SW low deselects the output drivers immediately (on the same cycle). Output selecting via a low on SS and high on SW at a rising CK clock has its effect on the output drivers after the next rising edge of the CK clock. Output drive is also controlled directly by output enable, G. G is an asynchronous input. No clock edges are required to enable/disable the out- put using G. Output data will be valid the latter of tGLQV and tKHQV. Out- puts will begin driving at tKHQX1. Outputs will hold previous data until tKHQX or tGHQX. WRITE AND BYTE WRITE FUNCTIONS Note that in the following discussion the term “byte” refers to nine bits of the RAM I/O bus. In all cases, the timing pa- rameters described for synchronous write input (SW) apply to each of the byte write enable inputs (SBa, SBb, etc.). Byte write enable inputs have no effect on read cycles. This allows the system designer not interested in performing byte writes to connect the byte enable inputs to active low (VSS). Reads of all bytes proceed normally and write cycles, activated via a low on SW, and the rising edge of the CK clock, write the entire RAM I/O width. This way the designer is spared having to drive multiple write input buffer loads. Byte writes are performed using the byte write enable in- puts in conjunction with the synchronous write input (SW). It is important to note that writing any one byte will inhibit a read of all bytes at the current address. The RAM cannot simulta- neously read one byte and write another at the same ad- dress. A write cycle initiated with none of the byte write enable inputs active is neither a read or a write. No write will occur, but the outputs will be deselected as in a normal write cycle. LATE WRITE The write address is sampled on the first rising edge of clock and write data is sampled on the following rising edge. The late write feature is implemented with single stage write buffering. Write buffering is transparent to the user. A comparator monitors the address bus and, when necessary, routes buffer contents to the outputs to assure coherent op- eration. This occurs in all cases whether there is a byte write or a full word is written. POWER UP AND INITIALIZATION The following supply voltage application sequence is rec- ommended: VSS, VDD, then VDDQ. Please note, per the Ab- solute Maximum Ratings table, VDDQ is not to exceed VDD + 0.5 V, whatever the instantaneous value of VDD. Once sup- plies have reached specification levels, a minimum dwell of 1.0 µs with C/K clock inputs cycling is required before begin- ning normal operations. |
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