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AM29BDS320GBD9VMI 데이터시트(PDF) 15 Page - SPANSION |
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15 / 74 page October 1, 2003 27243B1 Am29BDS320G 13 Prelimin ary Since the memory array is divided into four banks, each bank remains enabled for read access until the command register contents are altered. Address access time (tACC) is equal to the delay from stable addresses to valid output data. The chip enable access time (tCE) is the delay from the stable ad- dresses and stable CE# to valid data at the outputs. The output enable access time (tOE) is the delay from the falling edge of OE# to valid data at the output. The internal state machine is set for reading array data upon device power-up, or after a hardware reset. This ensures that no spurious alteration of the memory content occurs during the power transition. Requirements for Synchronous (Burst) Read Operation The device is capable of continuous sequential burst operation and linear burst operation of a preset length. When the device first powers up, it is enabled for asynchronous read operation. Prior to entering burst mode, the system should determine how many wait states are desired for the initial word (tIACC) of each burst access, what mode of burst operation is desired, which edge of the clock will be the active clock edge, and how the RDY signal will transition with valid data. The system would then write the burst mode configuration register command sequence. See “Set Burst Mode Configuration Register Command Sequence” and “Command Definitions” for fur- ther details. Once the system has written the “Set Burst Mode Configuration Register” com- mand sequence, the device is enabled for synchronous reads only. The initial word is output tIACC after the active edge of the first CLK cycle. Sub- sequent words are output tBACC after the active edge of each successive clock cycle, which automatically increments the internal address counter. Note that the device has a fixed internal address boundary that occurs every 64 words, starting at address 00003Fh. During the time the device is outputting data at this fixed internal address boundary (address 00003Fh, 00007Fh, 0000BFh, etc.), a two cycle latency occurs before data appears for the next address (address 000040h, 000080h, 0000C0h, etc.). The RDY output indicates this condition to the system by pulsing low. For standard handshaking devices, there is no two cycle latency between 3Fh and 40h (or addresses offset from 3F and 40h by a multiple of 64). See Table 10. For reduced wait-state handshaking devices, if the address latched is 3Dh (or off- set from 3Dh by a multiple of 64), an additional cycle latency occurs prior to the initial access. If the address latched is 3Eh (or offset from 3Eh by a multiple of 64) two additional cycle latency occurs prior to the initial access and the 2 cycle latency between 3Fh and 40h (or offset from 3Fh by a multiple of 64) will not oc- cur. For 3Fh latched addresses (or offset from 3Fh by a multiple of 64) three additional cycle latency occurs prior to the initial access and the 2 cycle latency between 3Fh and 40h (or offset from these addresses by a multiple of 64) will not occur. The device will continue to output sequential burst data, wrapping around to ad- dress 000000h after it reaches the highest addressable memory location, until the system drives CE# high, RESET# low, or AVD# low in conjunction with a new address. See Table 1, “Device Bus Operations,” on page 12. If the host system crosses the bank boundary while reading in burst mode, and the device is not programming or erasing, a two-cycle latency will occur as de- scribed above in the subsequent bank. If the host system crosses the bank |
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