I make a 29 programmer base on your board,but can not run on 1Mbps，only 115200

[happysoul]

I used auto routing software by "freerouting"

PCB
https://oshwhub.com/firseve/eeprom_29
Source code
https://gitee.com/happysoul/eeprom29

If i use 1000000 , read/write may lost byte. When read chip of MX29F040 512KB, but recived about 500K .
So i change baudrate to 115200, it looks well, somebody make this board and replace chip , routing , but only can run with 115200/2=57600

How to make a high speed programmer. Problem becouse of autorouting ?

[wagiminator]

Hi, unfortunately I can't tell you from a distance why it doesn't work with 1MHz UART BAUD. However, I can reassure you that this shouldn't be a problem when writing the EEPROM, UART is not the bottleneck here. You just don't reach full speed when reading.

[happysoul]

O.O Maybe use arduino language is the resion that can not reach full speed.
Like read 8bit, 8 times read each bit " digitalRead(Data0-8) ", then put 8bit into byte , return byte
Your code use PINC&PIND recive byte

[wagiminator]

Well, at least my code is very low-level optimized.