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FM25C160-GA Datasheet(PDF) 6 Page - Ramtron International Corporation |
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FM25C160-GA Datasheet(HTML) 6 Page - Ramtron International Corporation |
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6 / 13 page  FM25C160 - Automotive Temp. Rev. 3.1 July 2007 Page 6 of 13 RDSR - Read Status Register The RDSR command allows the bus master to verify the contents of the Status register. Reading Status provides information about the current state of the write protection features. Following the RDSR op- code, the FM25C160 will return one byte with the contents of the Status register. The Status register is described in detail in a later section. WRSR – Write Status Register The WRSR command allows the user to select certain write protection features by writing a byte to the Status register. Prior to issuing a WRSR command, the /WP pin must be high or inactive. Note that on the FM25C160, /WP only prevents writing to the Status register, not the memory array. Prior to sending the WRSR command, the user must send a WREN command to enable writes. Note that executing a WRSR command is a write operation and therefore clears the Write Enable Latch. The bus timing for RDSR and WRSR are shown below. Figure 7. RDSR Bus Timing Figure 8. WRSR Bus Timing Status Register & Write Protection The write protection features of the FM25C160 are multi-tiered. First, a WREN op-code must be issued prior to any write operation. Assuming that writes are enabled using WREN, writes to memory are controlled by the Status register. As described above, writes to the status register are performed using the WRSR command and subject to the /WP pin. The Status register is organized as follows. Table 2. Status Register Bit 7 6 5 4 3 2 1 0 Name WPEN 0 0 0 BP1 BP0 WEL 0 Bits 0 and 4-6 are fixed at 0 and cannot be modified. Note that bit 0 (/RDY in EEPROMs) is wired low since FRAM writes have no delay and the memory is never busy. All EEPROMs use Ready to indicate whether a write cycle is complete or not. The WPEN, BP1 and BP0 control write protection features. They are nonvolatile (shaded yellow). The WEL flag indicates the state of the Write Enable Latch. This bit is internally set by the WREN command and is cleared by terminating a write cycle (/CS high) or by using the WRDI command. BP1 and BP0 are memory block write protection bits. They specify portions of memory that are write protected as shown in the following table. Table 3. Block Memory Write Protection BP1 BP0 Protected Address Range 0 0 None 0 1 600h to 7FFh (upper ¼) 1 0 400h to 7FFh (upper ½) 1 1 000h to 7FFh (all) |
Similar Part No. - FM25C160-GA |
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Similar Description - FM25C160-GA |
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