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LJone.2
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April 13, 2021
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Source Current for Data Lines D0 - D7 and Address lines A0 - A9 - M48Z02

  • April 13, 2021
  • 1 reply
  • 699 views

I want to replace a 5114 or equivalent SRAM with the M48Z02 NVRAM to do away with batteries. As the 5114 has 4 data lines, the M48Z02 will have 4 'spare'. I want to pull those low, as well as A10, so if I need to, I can then use them for a second 5114 to allow access to the top half of the M48Z02 by setting a jumper on A10 to take it High. I can't determine the source current on the data pins and A10 from the data sheet, to be able determine a Pull Down Resistor value. There are four I values in table 8, 1uA, 2.3mA, 3mA and 80mA, but which one is the data source current. Thanks in advance.

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    Best answer by Peter BENSCH

    Welcome, @LJone.2​, at the community!

    It's not fully clear to me what you mean by emulating a 2nd 5114 since you only have one address bus and can only access one byte or nibble at a time. The first nibble (first four data lines) will also change if you are setting A10 to high and change the address at A0...A9.

    Perhaps it would make sense if you describe the task that the M48Z02 is supposed to do in a little more detail, preferably with a block diagram or, even better, an excerpt from a circuit diagram.

    However, it doesn't make sense to pull down data lines because they are driven by three-state output buffers that will be destroyed if you override them to the opposite level.

    Table 8 of the datasheet shows e.g. the TTL compatible output voltage levels at a certain test condition:

    • VOL = max 0.4V when sinking (driving Low with) a current of 2.1mA
    • VOH = min 2.4V when sourcing (driving High with) a current of -1mA

    The current of 1µA is the leakage current of the outputs (when the device is deselected) and the inputs, 3mA is the standby current and 80mA is the normal supply current the M48Z02 is drawing out of the supply voltage of 5V.

    Regards

    Peter

    1 reply

    P
    Peter BENSCHAnswer
    Technical Moderator
    April 13, 2021

    Welcome, @LJone.2​, at the community!

    It's not fully clear to me what you mean by emulating a 2nd 5114 since you only have one address bus and can only access one byte or nibble at a time. The first nibble (first four data lines) will also change if you are setting A10 to high and change the address at A0...A9.

    Perhaps it would make sense if you describe the task that the M48Z02 is supposed to do in a little more detail, preferably with a block diagram or, even better, an excerpt from a circuit diagram.

    However, it doesn't make sense to pull down data lines because they are driven by three-state output buffers that will be destroyed if you override them to the opposite level.

    Table 8 of the datasheet shows e.g. the TTL compatible output voltage levels at a certain test condition:

    • VOL = max 0.4V when sinking (driving Low with) a current of 2.1mA
    • VOH = min 2.4V when sourcing (driving High with) a current of -1mA

    The current of 1µA is the leakage current of the outputs (when the device is deselected) and the inputs, 3mA is the standby current and 80mA is the normal supply current the M48Z02 is drawing out of the supply voltage of 5V.

    Regards

    Peter

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