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25AA320X Datasheet(PDF) 6 Page - Microchip Technology |
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25AA320X Datasheet(HTML) 6 Page - Microchip Technology |
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6 / 24 page  25AA320/25LC320/25C320 DS21227E-page 6 2004 Microchip Technology Inc. 2.0 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 2-1. TABLE 2-1: PIN FUNCTION TABLE 2.1 Chip Select (CS) A low level on this pin selects the device. A high level deselects the device and forces it into Standby mode. However, a programming cycle which is already initiated or in progress will be completed, regardless of the CS input signal. If CS is brought high during a program cycle, the device will go into Standby mode as soon as the programming cycle is complete. When the device is deselected, SO goes to the high-impedance state, allowing multiple parts to share the same SPI bus. A low-to-high transition on CS after a valid write sequence initiates an internal write cycle. After power- up, a low level on CS is required prior to any sequence being initiated. 2.2 Serial Output (SO) The SO pin is used to transfer data out of the 25XX320. During a read cycle, data is shifted out on this pin after the falling edge of the serial clock. 2.3 Write-Protect (WP) This pin is used in conjunction with the WPEN bit in the Status register to prohibit writes to the nonvolatile bits in the Status register. When WP is low and WPEN is high, writing to the nonvolatile bits in the Status register is disabled. All other operations function normally. When WP is high, all functions, including writes to the nonvolatile bits in the Status register operate normally. If the WPEN bit is set, WP low during a Status register write sequence will disable writing to the Status register. If an internal write cycle has already begun, WP going low will have no effect on the write. The WP pin function is blocked when the WPEN bit in the Status register is low. This allows the user to install the 25XX320 in a system with WP pin grounded and still be able to write to the Status register. The WP pin functions will be enabled when the WPEN bit is set high. 2.4 Serial Input (SI) The SI pin is used to transfer data into the device. It receives instructions, addresses, and data. Data is latched on the rising edge of the serial clock. 2.5 Serial Clock (SCK) The SCK is used to synchronize the communication between a master and the 25XX320. Instructions, addresses, or data present on the SI pin are latched on the rising edge of the clock input, while data on the SO pin is updated after the falling edge of the clock input. 2.6 Hold (HOLD) The HOLD pin is used to suspend transmission to the 25XX320 while in the middle of a serial sequence with- out having to re-transmit the entire sequence again. It must be held high any time this function is not being used. Once the device is selected and a serial sequence is underway, the HOLD pin may be pulled low to pause further serial communication without resetting the serial sequence. The HOLD pin must be brought low while SCK is low, otherwise the HOLD function will not be invoked until the next SCK high-to- low transition. The 25XX320 must remain selected dur- ing this sequence. The SI, SCK, and SO pins are in a high-impedance state during the time the device is paused and transitions on these pins will be ignored. To resume serial communication, HOLD must be brought high while the SCK pin is low, otherwise serial communication will not resume. Lowering the HOLD line at any time will tri-state the SO line. Name PDIP SOIC 8-pin TSSOP 14-lead TSSOP Description CS 1 1 3 1 Chip Select Input SO 2 2 4 2 Serial Data Output NC — — — 3,4,5 Not Connected WP 3 3 5 6 Write-Protect Pin Vss 4 4 6 7 Ground SI 5 5 7 8 Serial Data Input SCK 6 6 8 9 Serial Clock Input NC — — — 10,11,12 Not Connected HOLD 7 7 1 13 Hold Input Vcc 8 8 2 14 Supply Voltage |
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