All of my code for the 8051 is written in C. However, I wish to re-write one of my Interrupt Handlers in Assembly language and have it interface with the rest of my program. Given the following C code, how do I convert it? I do not want to compile into an SRC file and then modify, I wish to simply do the whole routine in an assembly file.

void Ext0ISR(void) interrupt 0
{
byte value;

// double checking...
if (EXT0_PIN == 0)
{
value = MOD1_GetByte();
CLK_PIN = 0;
MOD2_SendByte( value );
CLK = 1;
}
}