LD HL,PC and CALL (HL)
                       ======================

It is possible to synthesise LD HL,PC and CALL (HL) by having a little
subroutine somewhere.

Code:
    LDHLPC:  E1  POP HL
    CALLHL:  E9  JP (HL)

Doing CALL LDHLPC does the equivalent of LD HL,PC.
Doing CALL CALLHL does the equivalent of CALL (HL).

I usually put this code at &000E-&000F when I'm writing non-Spectrum Z80
code.

You can do this on the ZX Spectrum with:
    CALL &006F        ; for CALL (HL)

    OR &FF:CALL &1FC6 ; for LD HL,PC

&1FC6 needs to be entered with the Z flag clear. The simplest way to do
this is to use an arithmetic instruction to set A to a non-zero value.
If you know what value A has in it, then comparing to a different value
will clear Z, for instance:

    CP   255   ; Assume A<>255, so clear Z
    CALL &1FC6

A LD HL,PC instruction is rarely needed on the ZX Spectrum as machine code
is entered with PUSH BC:RET so BC holds the entry address.


Another useful subroutine is CALL NZ,(HL) to call the address in HL if it
is non-zero, unfortunately this corrupts A:

    7C  LD  A,H
    B5  OR  L
    C8  RET Z
    E9  JP (HL)