| ??? 10/02/09 16:09 Read: times |
#169364 - 25MHz * 4bit = 12.5MB/s Responding to: ???'s previous message |
Richard Erlacher said:
Maarten Brock said:
Richard Erlacher said:
The [...] specification v1.9 [...] has a maximal clock rate of 25 MHz, and, therefore a data rate in 4-bit mode of 50 MBps, albeit in whatever bursts the SD card chooses to generate. Just out of curiosity, how does that work? You do mean 50 MByte/s don't you? Gee ... I thought it was obvious ... 25 Mbps * 4 ... in bursts, of course ... I guess I need to get out more ... Richard Erlacher said:
Now, if one uses built-in MCU features to handle SPI communication, the speed is considerably slower. The SD card spec indicates SPI can be used at up to 25 MHz. I'm not convinced the hardware support in any 805x-class MCU can handle that high a rate. All SiLabs chips including those up to 100 MHz can run SPI at 12.5 MHz. I know no faster SPI in an 8051. Maarten MBps = MegaBytes per second Mbps = Megabits per second RE But note that you did say 25MHz and 4-bit data width resulting in 50MB/s. I would have expected 12.5MB/s since it would take two transfers to get one byte. That was probably why Maarten Brock did react and wanted you to clarify the issue. |
