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Original question:

CD74HCT40105: EXPANSION, 8-BITS WIDE BY 16 N-BITS LONG USING.

CD74HCT40105: Replace SN74LS224 with CD74HCT40105

Hiroaki Yuyama TED
Expert 1720 points
Part Number: CD74HCT40105
Other Parts Discussed in Thread: SN74ALS232B

Dear, support team.

We replaced the SN74LS224 with the CD74HCT40105.
We are considering adding an inverting circuit to see if it can be replaced.

We would like to replace only the FIFO part without changing the timing and waveform of the peripheral input signal as much as possible.

I am attaching the EXCLE file for comparison.

Any advice would be appreciated.

FIFO_IC SN74LS224N　⇒　CD74HCT40105E.xlsx

Best Regards,
Hiroaki Yuyama

  • 0
    TI__Genius 12841 points

    Hi Hiroaki,

    Everything in the excel looks correct. The only thing I'm concerned about is on the SN74LS224A datasheet it shows word 1 being ready to read from the second it's loaded whereas for the CD74HCT40105 there seems to be a delay. (see below)

    The SN74LS224 is no longer carried by TI so I can't request one to test whether or not it experiences the same delay. That being said everything else appears to be similar enough that it wouldn't cause timing/waveform problems.

    Regards,

    Owen

  • 0 in reply to Owen Westfall
    Expert 1720 points

    Hi,Owen-san,
    Thank you for your answer.

    If you replace it with the CD74HCT40105, there will be a loading delay, but I understand that it is the closest model.
    We propose a circuit with a NOT circuit added to the CD74HCT40105.

    Best Regards,
    Hiroaki Yuyama

  • 0 in reply to Hiroaki Yuyama TED
    TI__Genius 12841 points

    Hi Hiroaki

    I'm confused by what you mean. Where in this do you intend to add the NOT circuit, and do you need any more help from me?

    Regards,

    Owen

  • 0 in reply to Owen Westfall
    Expert 1720 points

    Hi,Owen-san,
    Thank you for your support.

    I have an additional question from a customer.
    The NOT circuit I'm talking about is in the circuit inside the Excel link in the first post.
    Do you think it would be difficult to replace, including delay issues?

    In the SN74LS224A, looking at the LDCK and UNCK in the previous stage, the waveforms are 16-word intermediate extraction.

    CD74HCT40105 was assumed that reading would not be possible unless 16 words were read. Is this correct?

    The purpose of the replacement is to allow word-depth direction of FIFO registers.

    Can SN74LS224A have word-depth direction?
    If possible, please provide a reference circuit.

    Best Regards,
    Hiroaki Yuyama
  • 0 in reply to Hiroaki Yuyama TED
    TI__Genius 12841 points

    Hi Hiroaki,

    Hiroaki Yuyama TED said:
    Do you think it would be difficult to replace, including delay issues?

    No they look very very similar, and using the NOT gates should allow the input signals to go unchanged.

    Hiroaki Yuyama TED said:
    CD74HCT40105 was assumed that reading would not be possible unless 16 words were read. Is this correct?

    This is not correct. The first word can be read after waiting on the ~180ns delay it takes to ripple the data.

    For expanding in word depth direction. Everything appears to be correct for the CD74HCT40105.

    Again I cannot test the SN74LS224A however looking at the timing diagram by inserting a NOT gate instead of the Delay should allow for expansion in the depth direction.

    Regards,

    Owen

  • 0 in reply to Hiroaki Yuyama TED
    TI__Guru* 97046 points

    Hello Yuyama-san,

    Owen is current out of the office. I will ask him to respond when he returns tomorrow.

  • 0 in reply to Emrys Maier
    Expert 1720 points

    Hello, Owen-san and Emrys-san,

    Thank you for your kind support.

    When we replace SN74LS224A with CD74HCT40105 for customer, is it possible word-depth direction of FIFO registers?

    I would like to know if the word-depth direction of FIFO registers is possible by adding a NOT circuit to the SI and SO terminals, except for the 180nsec delay of the CD74HCT40105.

    Best Regards,
    Hiroaki Yuyama

  • 0 in reply to Hiroaki Yuyama TED
    TI__Genius 12841 points

    Hi Hiroaki

    Hiroaki Yuyama TED said:
    I would like to know if the word-depth direction of FIFO registers is possible by adding a NOT circuit to the SI and SO terminals, except for the 180nsec delay of the CD74HCT40105.

    Yes the image at the bottom of the excel will expand in the word depth direction for the CD74HCT40105.

    Regards,

    Owen

  • 0 in reply to Owen Westfall
    Expert 1720 points

    Hi,Owen-san,
    Thank you for your support.

    Regarding the replacement of CD74HCT40105 from SN74LS224A, there is a problem of 180nsec delay, but I understood that it can be used as word-depth direction of FIFO registers by adding a NOT circuit.
    I add the NOT circuit and suggest the CD74HCT40105 to the customer.

    Best Regards,
    Hiroaki Yuyama

  • 0 in reply to Hiroaki Yuyama TED
    Expert 1720 points

    Hi,Owen-san,
    Thank you for your support.

    A customer says that the datasheet for the CD74HCT40105 does not mention the word depth direction.
    Probably, The CD74HCT40105 does not have a word depth direction timing chart, and it says that it cannot be read unless it is recorded after all 16 words are complete.

    Do you have any application notes or reference circuits for the CD74HCT40105 word depth direction timing chart, or have you used it with other customers?

    For example, for the same 16 × 4 ASYNCHRONOUS FIRST-IN, FIRST-OUT MEMORY SN74ALS232B, the description on the front cover of the datasheet says “Cascading is easily accomplished in the word-width direction but is not possible in the word-depth direction.” have a description
    www.ti.com/.../sn74als232b

    We do not have definitive information available for the word-depth direction of CD74HCT40105.

    Best Regards,
    Hiroaki Yuyama

  • 0 in reply to Hiroaki Yuyama TED
    TI__Genius 12841 points

    Hi Hiroaki,

    In the data sheet figure 12 is an example of it being expanded in the word depth. 

    It is supported, and the 16 words don't have to be read for the first word to be ready. There is only a slight delay due to the data needing to ripple down through the registers.

    Hiroaki Yuyama TED said:
    Do you have any application notes or reference circuits for the CD74HCT40105 word depth direction timing chart, or have you used it with other customers?

    We do not have one.

    Regards,

    Owen

  • 0 in reply to Owen Westfall
    Expert 1720 points

    Hi, Owen-san,
    Thank you for your great support.

    We understand In the data sheet figure 12 is an example of it being expanded in the word depth.
    We ask customers to understand the word-depth direction in Figure 12.
    We suggest the customer to replace the SN74LS224A with the CD74HCT40105 by adding a NOT gate.

    Best Regards,
    Hiroaki Yuyama