Cypress CY14B101P manual SPI Operating Features, SPI Functional Description

PRELIMINARYCY14B101P

SPI Operating Features

Power Up

Power up is defined as the condition when the power supply is turned on and VCC crosses Vswitch voltage. During this time, the Chip Select (CS) must be enabled to follow the VCC voltage. Therefore, CS must be connected to VCC through a suitable pull up resistor. As a built in safety feature, Chip Select (CS) is both edge sensitive and level sensitive. After power up, the device is not selected until a falling edge is detected on Chip Select (CS). This ensures that Chip Select (CS) must have been HIGH, before going Low to start the first operation.

As described earlier, nvSRAM performs a Power Up Recall operation after power up and therefore, all memory accesses are disabled for tRECALL duration after power up. The HSB pin can be probed to check the ready/busy status of nvSRAM after power up.

Power On Reset

A Power On Reset (POR) circuit is included to prevent inadvertent writes. At power up, the device does not respond to any instruction until the VCC reaches the Power On Reset threshold voltage (VSWITCH). After VCC transitions the POR threshold, the device is internally reset and performs a Power Up Recall operation. The device is in the following state after POR:

■Deselected (after Power up, a falling edge is required on Chip Select (CS) before any instructions are started).

■Standby Power mode

■Not in the Hold Condition

■Status register state:

❐Write Enable (WEN) bit is reset to 0.

❐WPEN, BP1, BP0 unchanged from previous power down

The WPEN, BP1, and BP0 bits of the Status Register are nonvol- atile bits and remain unchanged from the previous power down.

Before selecting and issuing instructions to the memory, a valid and stable VCC voltage must be applied. This voltage must remain valid until the end of the transmission of the instruction.

Power Down

At power down (continuous decay of VCC), when VCC drops from the normal operating voltage and below the VSWITCH threshold voltage, the device stops responding to any instruction sent to it. If a write cycle is in progress during power down, it is allowed tDELAY time to complete after Vcc transitions below VSWITCH. After this, all memory accesses are inhibited and a conditional AutoStore operation is performed (AutoStore is not performed if no writes have happened since last RECALL cycle). This feature prevents inadvertent writes to nvSRAM from happening during power down.

However, to avoid the possibility of inadvertent writes during power down, ensure that the device is deselected and is in Standby Power Mode, and the Chip Select (CS) follows the voltage applied on VCC.

Active Power and Standby Power Modes

When Chip Select (CS) is LOW, the device is selected, and is in the Active Power mode. The device consumes ICC current, as specified in DC Electrical Characteristics on page 22. When Chip Select (CS) is HIGH, the device is deselected and the device goes into the Standby Power mode if a STORE or RECALL cycle is not in progress. If a STORE/RECALL cycle is in progress, the device goes into the Standby Power Mode after the STORE/RECALL cycle is completed. In the Standby Power mode the current drawn by the device drops to ISB.

SPI Functional Description

The CY14B101P uses an 8-bit instruction register. Instructions and their operation codes are listed in Table 2. All instructions, addresses, and data are transferred with the MSB first and start with a HIGH to LOW CS transition. There are, in all, 12 SPI instructions which provide access to most of the functions in nvSRAM. Further, the WP and HOLD pins provide additional functionality driven through hardware.

Table 2. Instruction Set

Instruction	Instruction	Opcode	Operation
Category	Name
	WREN	0000 0110	Set Write Enable
			Latch
Status	WRDI	0000 0100	Reset Write
			Enable Latch
Register
	RDSR	0000 0101	Read Status
Instructions
			Register
	WRSR	0000 0001	Write Status
			Register
SRAM	READ	0000 0011	Read Data From
			Memory Array
Read/Write
	WRITE	0000 0010	Write Data To
Instructions
			Memory Array
RTC	WRTC	0001 0010	Write RTC
			Registers
Read/Write
	RDRTC	0001 0011	Read RTC
Instructions
			Registers
	STORE	0011 1100	Software Store
Special NV	RECALL	0110 0000	Software Recall
Instructions	ASENB	0101 1001	AutoStore Enable
	ASDISB	0001 1001	AutoStore Disable
Reserved	- Reserved -	0001 1110	Reserved for
			Internal use

The SPI instructions in CY14B101P are divided based on their functionality in following types:

❐Status Register Access: WRSR and RDSR instructions

❐Write Protection Functions: WREN and WRDI instructions along with WP pin and WEN, BP0 and BP1 bits

❐SRAM memory Access: READ and WRITE instructions

❐RTC access: RDRTC and WRTC instructions

❐nvSRAM special instructions: STORE, RECALL, ASENB and

ASDISB

Document #: 001-44109 Rev. *B Page 7 of 32

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