TTL TO RS 232

HI, I am super confused why we need to use ttl to rs 232 conversion and rs232 to ttl conversion. please help...
8051 in TTL-LOGIC

I'm just starting on a "8051 in TTL-logic"-design. Is this ever done before? I hope to present the results so far on my site by Tuesday. Any comment is welcome.
8051 in TTL-LOGIC

I'm just starting on a "8051 in TTL-logic"-design. Is this ever done before? I hope to present the results so far on my site by Tuesday. Any comment is welcome.
TTL TO RS 232

HI, I am super confused why we need to use ttl to rs 232 conversion and rs232 to ttl conversion. please help...
3.3V supply for ttl/rs232

Hi, I find a problem when I wanted to run a ATMEGA32 with VCC supply of 3.3V, everything is okay except USART. I see that if supply voltage is 5V then USART works well. With the same ttl/rs232 module...