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FM25CL04-S Folha de dados(PDF) 7 Page - Ramtron International Corporation |
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FM25CL04-S Folha de dados(HTML) 7 Page - Ramtron International Corporation |
7 / 12 page N O T R EC O M ME N D ED FO R N EW D ES IG N S R ep la ce d by FM 25 L0 4 Rev. 3.1 May 2005 Page 7 of 12 Table 3. Block Memory Write Protection BP1 BP0 Protected Address Range 0 0 None 0 1 180h to 1FFh (upper ¼) 1 0 100h to 1FFh (upper ½) 1 1 000h to 1FFh (all) The BP1 and BP0 bits allow software to selectively write protect the array. These settings are only used when the /WP pin is inactive and the WREN command has been issued. The following table summarizes the write protection conditions. Table 4. Write Protection WEL /WP Protected Blocks Unprotected Blocks Status Register 0 X Protected Protected Protected 1 0 Protected Protected Protected 1 1 Protected Unprotected Unprotected Memory Operation The SPI interface, which is capable of a relatively high clock frequency, highlights the fast write capability of the FRAM technology. Unlike SPI-bus EEPROMs, the FM25CL04 can perform sequential writes at bus speed. No page register is needed and any number of sequential writes may be performed. Write Operation All writes to the memory array begin with a WREN op-code. The next op-code is the WRITE instruction. This op-code must include the address MSB. It is followed by a single byte address value. In total, the 9-bits specify the address of the first byte of the write operation. Subsequent bytes are data and they are written sequentially. Addresses are incremented internally as long as the bus master continues to issue clocks. If the last address of 1FFh is reached, the counter will roll over to 000h. Data is written MSB first. A write operation is shown in Figure 9. Unlike EEPROMs, any number of bytes can be written sequentially and each byte is written to memory immediately after it is clocked in (after the 8 th clock). The rising edge of /CS terminates a WRITE op-code operation. Asserting /WP active in the middle of a write operation will have no effect until the byte being written has completed. Read Operation After the falling edge of /CS, the bus master can issue a READ op-code. This op-code must include the address MSB. It is followed by a single byte address value. In total, the 9-bits specify the address of the first byte of the read operation. After the op-code and address are complete, the SI line is ignored. The bus master issues 8 clocks, with one bit read out for each. Addresses are incremented internally as long as the bus master continues to issue clocks. If the last address of 1FFh is reached, the counter will roll over to 000h. Data is read MSB first. The rising edge of /CS terminates a READ op-code operation. A read operation is shown in Figure 10. Hold The /HOLD pin can be used to interrupt a serial operation without aborting it. If the bus master pulls the /HOLD pin low while SCK is low, the current operation will pause. Taking the /HOLD pin high while SCK is low will resume an operation. The transitions of /HOLD must occur while SCK is low, but the SCK and /CS pins can toggle during a hold state. Figure 9. Memory Write |
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