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HSB pin as implemented in nvSRAMs

Posted: 20 Oct 2008     Print Version  Bookmark and Share

Keywords:HSB  nvSRAM  AutoStore  store cycle 

The hardware store busy (HSB) pin is a bi-directional pin with multiple functions in Cypress nvSRAMs. The HSB is used to:

  • • Indicate that a store cycle is in progress
  • • Initiate a store cycle
  • • Indicate that Vcc has transitioned down through VSWITCH
  • The HSB output has a strong n-channel pull down transistor and a small p-channel pull up transistor. The p-channel pull up transistor holds the HSB high, as long as there are no external loads placed on the pin. In this scenario, the HSB acts as an open drain output. Internally, the HSB p-channel pull up is connected to Vcc. The HSB can be left unconnected if not used. The controller cannot access the nvSRAM when the HSB pin is low. The HSB pin is actively pulled low when the nvSRAM executes a store cycle and remains low till the store cycle is complete. The controller can determine the end of the store cycle by monitoring the HSB pin.

    When the HSB is externally pulled low by the system, the device executes a store only if a WRITE to the SRAM has occurred since the last store or recall. When the system Vcc collapses or transitions through VSWITCH, if there is a WRITE to the SRAM since the last store or recall, the device executes AutoStore.

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