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TCA8418: TCA8418RTWR Key Scan Issue

Onur Göksu
Prodigy 15 points
Part Number: TCA8418

Tool/software:

Hi all,

We have a custom iM.X8MQ board and a keypad circuit connected to it, including TCA8418RTWR. 

Configured Registers:

0x01 -> 0x19 (tca8418_keypad driver does so)
0x1D -> 0x0F (4 rows)
0x1E -> 0x0F (4 cols)

And I have been dealing with the datasheets and documents, currently I have some confusions. 

1) "TCA8418 I 2C Controlled Keypad Scan IC With Integrated ESD Protection" page 37 has this statement below: 

In the keypad setup in Figure 26, there is a 4x3 keypad matrix, connected to ROW0-ROW3, and COL0-COL2. All of the ROWs are configured as inputs with pullup resistors. The COLs are configured as outputs, driving low. When a key press is made, one of the ROW inputs will be pulled low, letting the TCA8418 know that a key has been pressed, and the TCA8418 will then start the key scanning algorithm. During this algorithm, It sweeps the output low across the columns, such that only 1 column is driven low at a time. While this is done to each column, the TCA8418 will read the ROW inputs, to determine which keys on a column are being pressed.

So, in the idle connection we have our ROWx pins HIGH, pulled-up internally and COLx pins LOW.

After pressing a key, a ROWx pin should be pulled LOW. 

Then, the statement tells us the IC will execute a "sweep" the output low for the columns, but don't they have all LOW signals? What's the meaning of this? How could IC tell which button is pressed in ROWx?

2) ROWx is pulled-up in the idle scan connection. So, how pressing a button make a pull-down or a LOW signal happen there? I couldn't understand the ROWx-button-COLx relationship. Could anyone elaborate?

The current setup of ours works like below:

Pressing a keypad button doesn't change ROWx status, all rows stay HIGH.

COLx goes HIGH.

No scan occurs.

INT stays HIGH all the time.

3) Idk if it's related or indicating any error,  GPIO_DAT_STAT1–3 (Address 0x14–0x16) has values of 0xFF, 0xFF and 0x03 and I cannot clear or rewrite them.

Thanks in advance,

Onur

  • 0
    Guru 316690 points

    You have not shown the schematic.

    1. The datasheet says that "only 1 column is driven low at a time". When a row input is low, the pressed key must be in that column.

    2. Pressing a key connects the row to the column. With a weak pull-up resistor and the COLx output strongly pulling low, the result is low.

    3. GPIOs are not keys.

    4. Please note that all registers must be configured correctly and consistenly.

  • 0
    TI__Mastermind 40136 points

    Hi Onur,

    The team is out today as today is a US Holiday. We will get back to you early next week. Thank you for understanding.

    Regards,

    Jack

  • 0
    TI__Mastermind 47328 points

    Hi Onur,

    Onur Göksu said:

    1) "TCA8418 I 2C Controlled Keypad Scan IC With Integrated ESD Protection" page 37 has this statement below: 

    In the keypad setup in Figure 26, there is a 4x3 keypad matrix, connected to ROW0-ROW3, and COL0-COL2. All of the ROWs are configured as inputs with pullup resistors. The COLs are configured as outputs, driving low. When a key press is made, one of the ROW inputs will be pulled low, letting the TCA8418 know that a key has been pressed, and the TCA8418 will then start the key scanning algorithm. During this algorithm, It sweeps the output low across the columns, such that only 1 column is driven low at a time. While this is done to each column, the TCA8418 will read the ROW inputs, to determine which keys on a column are being pressed.

    So, in the idle connection we have our ROWx pins HIGH, pulled-up internally and COLx pins LOW.

    After pressing a key, a ROWx pin should be pulled LOW. 

    Then, the statement tells us the IC will execute a "sweep" the output low for the columns, but don't they have all LOW signals? What's the meaning of this? How could IC tell which button is pressed in ROWx?

    The key is that only 1 column is driven LOW at a single time. It sweeps each COL individually not all at the same time. 

    Onur Göksu said:

    2) ROWx is pulled-up in the idle scan connection. So, how pressing a button make a pull-down or a LOW signal happen there? I couldn't understand the ROWx-button-COLx relationship. Could anyone elaborate?

    The current setup of ours works like below:

    Pressing a keypad button doesn't change ROWx status, all rows stay HIGH.

    COLx goes HIGH.

    No scan occurs.

    INT stays HIGH all the time.

    A Row is connected to the Col pin via a switch that is open-circuit. 

    If a ROW is weakly pulled-up HIGH, and a COL is driven strongly LOW, the COL pin output will pull the weak ROW input down when the switch press connects the ROW to COL. ROW and COL will be the same state when the switch is pressed. 

    When the switch is not pressed, the ROW is input w/ PU resistor, so the ROW pin is HIGH logic. 

    The COL is output LOW, but since the switch is open-circuit, the ROW input stays HIGH logic meaning the switch was not pressed. 

    Ensure that KE_IEN = 1 for interrupt to be asserted on /INT when a key event occurs. 

    Onur Göksu said:
    3) Idk if it's related or indicating any error,  GPIO_DAT_STAT1–3 (Address 0x14–0x16) has values of 0xFF, 0xFF and 0x03 and I cannot clear or rewrite them.

    If the I/O's are being used in keypad scanning mode, they need to be set to "1" in the KP_GPIOx registers. The default value is "0" making all the ROW and COL pins individually controlled I/O's rather than keypad scanning. 

    GPIO_DAT_STAT is specific to pins set to GPIO mode. Not keypad scanning mode. 

    Regards,

    TYler