STM8S I2C Master Missing ACK
There are two standard formats for 7-bit I2C addresses -- 0x7F and 0xFE. It looks like I2C_Send7bitAddress() expects 0xFE format. If your actual slave address is 0x30, try sending 0x60 (which is 0x30 &lt;&lt; 1) and see if that works.

The reason for the 0xFE format is that it lets you treat the read/write direction bit as part of the slave address, giving an 8-bit value. That's what you actually see on the bus.