芯片地址上写零是什么是应答，还是就是地址

void set_address(void)
{
D12_SetAddressEnable((unsigned char)(ControlData.DeviceRequest.wValue &
DEVICE_ADDRESS_MASK), 1);
single_transmit(0, 0);
}
void single_transmit(unsigned char * buf, unsigned char len)
{
if( len <= EP0_PACKET_SIZE) {
D12_WriteEndpoint(1, len, buf);
}
}
unsigned char D12_WriteEndpoint(unsigned char endp, unsigned char len, unsigned char  * buf)
{
unsigned char i;

if(bEPPflags.bits.in_isr == 0)
DISABLE;
//---------------------
outportcmd(endp); //选择端点
inportb(); //读入满/空状态

outportcmd(0xF0); //<写缓冲区>命令
outportdata(0);
outportdata(len);

for(i=0; i<len; i++)
outportdata(*(buf+i));

outportcmd(0xFA); //《使缓冲区有效>有下一个IN来时可以发送

//--------------------------------
if(bEPPflags.bits.in_isr == 0)
ENABLE;

return len;
}

往芯片上写零是什么是应答，还是就是地址