Differences

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--- reprap:anet:anet_mainboard_overclocking [2018/01/04 15:30] – gmarsh23
+++ reprap:anet:anet_mainboard_overclocking [2018/01/04 15:41] – [Crystal selection and replacement] gmarsh23
@@ Line 72: / Line 72: @@
 If you're using the USB interface of the printer, using Octoprint for example, the crystal you choose affects how accurate the baud rate of the Mega1284P's UART will be at a given baud rate. For reliability reasons this should not exceed +-5%; ideally this value is less than +-2.5%. If you only printing from the SD card, this isn't an issue.
-^ MHz (below), baud (right) ^ 115200 ^ 230400 ^ 250000 ^ 460800 ^ 500000 ^ 921600 ^ 1000000 ^ 1500000 ^
+^ Crystal freq (below), baud (right) ^ 115200 ^ 230400 ^ 250000 ^ 460800 ^ 500000 ^ 921600 ^ 1000000 ^ 1500000 ^
-| 16 | 2.1% | -3.5% | 0% | 8.5% | 0% | 8.5% | 0% | 33% |
+| 16MHz | 2.1% | -3.5% | 0% | //8.5%// | 0% | //8.5%// | 0% | //33%// |
-| 20 | -1.4% | -1.4% | 0% | 8.5% | 0% | -9.6% | -16.7% | -16.7% |
+| 20MHz | -1.4% | -1.4% | 0% | //8.5%// | 0% | //-9.6%// | //-16.7%// | //-16.7%// |
-| 24 | 0.16% | 0.16% | 0% | -7.0% | **0%** | 8.5% | 0% | 0% |
+| 24MHz | 0.16% | 0.16% | 0% | //-7.0%// | **0%** | //8.5%// | 0% | 0% |
-| 25 | 0.5% | -3.1% | -3.8% | -3.1% | 4.2% | 13% | 4.2% | 4.2% |
+| 25MHz | 0.5% | -3.1% | -3.8% | -3.1% | 4.2% | //13%// | 4.2% | 4.2% |
-| 27 | 1% | -2.3% | -3.6% | 4.6% | -3.6% | 8.4% | 12.5% | 12.5% |
+| 27MHz | 1% | -2.3% | -3.6% | 4.6% | -3.6% | //8.4%// | //12.5%// | //12.5%// |
 To calculate for different clock frequencies and baud rates, use the following math:
-  * UART divisor = (Processor clock) / 8 / Desired baud rate
+  * UART divisor = crystal frequency / 8 / Desired baud rate
-  * Actual baud rate = (Processor clock) / 8 / rounded divisor value
+  * Actual baud rate = crystal frequency / 8 / rounded divisor value
   * Actual baud rate and desired baud rate should be +-5%, preferably +-2.5%
@@ Line 178: / Line 178: @@
   #define DELAY_9_NOP DELAY_1_NOP; DELAY_8_NOP
-Lastly, find the following section:
+Next find the following section:
   #if CYCLES_PER_MICROSECOND == 16
@@ Line 186: / Line 186: @@
   #endif
-Add the two middle lines shown, with the values altered to correspond to the crystal frequency you've chosen. Here is the setting for 24MHz - Note that "DELAY_20_NOP" and "DELAY_4_NOP" add up to 24.
+Add the two additional lines shown (the #elif line and the line after), with the "24" value altered to correspond to the crystal frequency you've chosen. Here is the setting for 24MHz - Note that "DELAY_20_NOP" and "DELAY_4_NOP" add up to 24. If you're using a frequency that isn't a multiple of 1MHz, then round up (eg, use 25 for a 24.576MHz crystal)
   #if CYCLES_PER_MICROSECOND == 16
@@ Line 222: / Line 222: @@
   python createSpeedLookupTable.py --cpu-freq 25 > new_table.h
-If you're using a crystal frequency which isn't a multiple of 1MHz, you'll need to edit the script to remove the "* 1000000" line, and call the script with --cpu-freq <hz> instead.
+If you're using a crystal frequency which isn't a multiple of 1MHz, you'll need to edit the script to remove the "* 1000000", and call the script with --cpu-freq <hz> instead.
 ==== Compiling and installing new firmware ====
 There are many guides online describing how to compile and install Marlin on an Anet A8. Find one and link it here :)