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| 01:20.18 | prpplague | dfarnsworth: ping |
| 01:40.02 | prpplague | CosmicPenguin: give me a ping when you can |
| 02:09.40 | g1powermac | hey prpplague |
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| 11:02.36 | mne | Hi. Can someone explain to me how the bidirectional SD-Bus interface works with SD-cards ? In the bidirectional communication, it is not clear to me when the host pins should be configured as output pins and when they should be input pins. |
| 11:03.07 | mne | That is, for obvious reasons, the SD card and the host can not drive the lines at the same time |
| 11:03.48 | av500 | its part of the SD protocol specs |
| 11:05.25 | mne | I had a look at them, but they only mention that the pins are bi-directional. I could not find the part where it mentions *when* a pin is output and when it is configured as input |
| 11:06.25 | mne | I have the "SD specifications - Part1 - Physical Layer Simplified Specification" here ... |
| 11:08.02 | mne | In addition, I have the "SanDisk SD Card Product Manual 2.2" |
| 11:09.42 | mne | In the "SD Card Interface Description" is says, that the data and CMD lines are used bidirectionally |
| 11:09.49 | mne | and push/pull is mentioned |
| 11:10.21 | mne | But I don't understand how I should interface these lines to my microcontroller. I can either configure a pin as output or as input .. |
| 11:11.08 | mne | Or I could configure the pin as input and just switch the pull-up/pull-down resistors |
| 11:11.33 | mne | "Data lines are bi-directional signals. Host and card drivers are operating in push-pull mode." |
| 11:13.09 | av500 | no |
| 11:13.14 | av500 | you have to implement the protocal |
| 11:13.16 | av500 | protocol |
| 11:13.23 | av500 | and switch from in to out |
| 11:13.27 | av500 | at the right time |
| 11:14.07 | av500 | read the specs |
| 11:14.25 | mne | Sure I have to switch between input and output mode, but the spec doesn't make it clear when .. |
| 11:14.50 | mne | to which part of the spec are you referring exactly ? I have it in front of me and it doesn't mention when to switch .. |
| 11:14.51 | av500 | then you have the wrong specs |
| 11:14.56 | av500 | or incomplete ones |
| 11:15.11 | mne | I have the two specs I mentioned above. Do you have another one ? |
| 11:16.08 | av500 | I am sure the SD spec mentions how the protocol works |
| 11:20.44 | mne | https://www.sdcard.org/downloads/pls/simplified_specs/Part_1_Physical_Layer_Simplified_Specification_Ver_3.01_Final_100518.pdf |
| 11:22.32 | mne | Thes pec doesn't mention it ... |
| 11:22.45 | mne | However, I have an idea how it *might* work .. |
| 11:22.46 | av500 | well, I will not read a 150page spec for you... |
| 11:23.55 | mne | It's explained in the "SD Bus" section that has 4 pages. And I read through them and it is not mentioned when the line is input and when it is output |
| 11:24.02 | mne | Anyway, my idea how it might work: |
| 11:24.18 | mne | Initially, all lines are configured as input |
| 11:24.25 | mne | The host acts as master |
| 11:24.48 | mne | So when it wants to start a data transfer, it just drives the lines for the duration of data transfer |
| 11:25.01 | mne | after that, it immediately sets back all input lines to input |
| 11:25.39 | mne | The CLK line is just an input |
| 11:25.46 | av500 | output |
| 11:25.58 | mne | from the cards perspective, it's an input |
| 11:26.19 | av500 | yes |
| 11:26.51 | mne | so, by controlling the CLK, I believe that I can make sure that the card doesn't drive the output when the host is still driving it |
| 11:27.20 | mne | And since the card is just a slave device, it is not considered to transmit something on the bus "out of the blue" |
| 11:27.27 | av500 | exactly |
| 11:27.30 | mne | But only after a request sent by the master |
| 11:27.34 | av500 | yep |
| 11:27.44 | mne | So, this is how I believe it might work .. |
| 11:28.10 | mne | But it's still not mentioned in the specs. Maybe because it is "so obvious" :P |
| 11:31.19 | av500 | maybe |
| 11:31.20 | av500 | bbl |
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| 17:28.08 | gandhijee_ | <PROTECTED> |
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| 23:50.11 | landley | gandhijee_: CFLAGS ="-m 32" make |