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NM93C46TVM8 Datasheet(PDF) 6 Page - Fairchild Semiconductor |
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NM93C46TVM8 Datasheet(HTML) 6 Page - Fairchild Semiconductor |
6 / 13 page 6 www.fairchildsemi.com NM93C46 Rev. E Functional Description A typical Microwire cycle starts by first selecting the device (bringing the CS signal high). Once the device is selected, a valid Start bit (“1”) should be issued to properly recognize the cycle. Following this, the 2-bit opcode of appropriate instruction should be issued. After the opcode bits, the 6-bit address information should be issued. For certain instructions, some of these 6 bits are don’t care values (can be “0” or “1”), but they should still be issued. Following the address information, depending on the instruction (WRITE and WRALL), 16-Bit data is issued. Otherwise, depend- ing on the instruction (READ), the device starts to drive the output data on the DO line. Other instructions perform certain control functions and do not deal with data bits. The Microwire cycle ends when the CS signal is brought low. However during certain instructions, falling edge of the CS signal initiates an internal cycle (Programming), and the device remains busy till the completion of the internal cycle. Each of the 7 instructions is explained in detail in the following sections. 1) Read (READ) READ instruction allows data to be read from a selected location in the memory array. Input information (Start bit, Opcode and Address) for this instruction should be issued as listed under Table1. Upon receiving a valid input information, decoding of the opcode and the address is made, followed by data transfer from the selected memory location into a 16-bit serial-out shift register. This 16-bit data is then shifted out on the DO pin. D15 bit (MSB) is shifted out first and D0 bit (LSB) is shifted out last. A dummy-bit (logical 0) precedes this 16-bit data output string. Output data changes are initiated on the rising edge of the SK clock. After reading the 16-bit data, the CS signal can be brought low to end the Read cycle. Refer Read cycle diagram. 2) Write Enable (WEN) When VCC is applied to the part, it “powers up” in the Write Disable (WDS) state. Therefore, all programming operations must be preceded by a Write Enable (WEN) instruction. Once a Write Enable instruction is executed, programming remains enabled until a Write Disable (WDS) instruction is executed or V CC is completely removed from the part. Input information (Start bit, Opcode and Address) for this WEN instruction should be issued as listed under Table1. The device becomes write-enabled at the end of this cycle when the CS signal is brought low. Execution of a READ instruction is independent of WEN instruction. Refer Write Enable cycle diagram. 3) Write (WRITE) WRITE instruction allows write operation to a specified location in the memory with a specified data. This instruction is valid only when I Device is write-enabled (Refer WEN instruction) Input information (Start bit, Opcode, Address and Data) for this WRITE instruction should be issued as listed under Table1. After inputting the last bit of data (D0 bit), CS signal must be brought low before the next rising edge of the SK clock. This falling edge of the CS initiates the self-timed programming cycle. It takes tWP time (Refer appropriate DC and AC Electrical Characteristics table) for the internal programming cycle to finish. During this time, the device remains busy and is not ready for another instruction. The status of the internal programming cycle can be polled at any time by bringing the CS signal high again, after tCS interval. When CS signal is high, the DO pin indicates the READY/BUSY status of the chip. DO = logical 0 indicates that the programming is still in progress. DO = logical 1 indicates that the programming is finished and the device is ready for another instruction. It is not required to provide the SK clock during this status polling. While the device is busy, it is recommended that no new instruction be issued. Refer Write cycle diagram. It is also recommended to follow this instruction (after the device becomes READY) with a Write Disable (WDS) instruction to safeguard data against corruption due to spurious noise, inadvert- ent writes etc. 4) Write All (WRALL) Write all (WRALL) instruction is similar to the Write instruction except that WRALL instruction will simultaneously program all memory locations with the data pattern specified in the instruction. This instruction is valid only when I Device is write-enabled (Refer WEN instruction) Input information (Start bit, Opcode, Address and Data) for this WRALL instruction should be issued as listed under Table1. After inputting the last bit of data (D0 bit), CS signal must be brought low before the next rising edge of the SK clock. This falling edge of the CS initiates the self-timed programming cycle. It takes t WP time (Refer appropriate DC and AC Electrical Characteristics table) for the internal programming cycle to finish. During this time, the device remains busy and is not ready for another instruction. Status of the internal programming can be polled as described under WRITE instruction description. While the device is busy, it is recommended that no new instruction be issued. Refer Write All cycle diagram. 5) Write Disable (WDS) Write Disable (WDS) instruction disables all programming opera- tions and should follow all programming operations. Executing this instruction after a valid write instruction would protect against accidental data disturb due to spurious noise, glitches, inadvertent writes etc. Input information (Start bit, Opcode and Address) for this WDS instruction should be issued as listed under Table1. The device becomes write-disabled at the end of this cycle when the CS signal is brought low. Execution of a READ instruction is indepen- dent of WDS instruction. Refer Write Disable cycle diagram. 6) Erase (ERASE) The ERASE instruction will program all bits in the specified location to a logical “1” state. Input information (Start bit, Opcode and Address) for this WDS instruction should be issued as listed under Table1. After inputting the last bit of data (A0 bit), CS signal must be brought low before the next rising edge of the SK clock. This falling edge of the CS initiates the self-timed programming cycle. It takes t WP time (Refer appropriate DC and AC Electrical Characteristics table) for the internal programming cycle to finish. During this time, the device remains busy and is not ready for another instruction. Status of the internal programming can be polled as described under WRITE instruction description. While the device is busy, it is recommended that no new instruction be issued. Refer Erase cycle diagram. |
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