Apparently, this is not the case anymore.

See the quote from C-manual in my previous post. According to the changelog, this was introduced in C51 version 6.00.

I tried the following snippet in the eval version 7.50:

enum {x, y, z} ee;

main()
{
  ee = y;
  ee++;
  ee = 1234;
}

It threw the following warning:

ASDFG.C(27): warning C259: '=': different enumeration types

referring to the line where 1234 is assigned to the enum variable ee (apparently, the variable is char so 1234 won't match); and (part of) the resulting binary (as displayed in the simulator) is:

    25:   ee = y; 
C:0x08A3    750801   MOV      ee(0x08),#0x01
    26:   ee++; 
C:0x08A6    0508     INC      ee(0x08)
    27:   ee = 1234; 
C:0x08A8    7508D2   MOV      ee(0x08),#0xD2
    28: } 
C:0x08AB    22       RET      

JW