Specifications

Processor Description (V40)
Strings are addressed differently from other variables. The
segment register used to point to the source string is DS0 [DS],
unless an override is used. The offset for the string source is the
IX [SI] register. The segment register for the string destination is
always DS1 [ES] and the offset is specified in IY [DI].
Table 5-1
Segment Registers.
Memory Default Alternate
Reference Segment Segment Offset
Instruction Fetch PS[CS] NONE PFP[IP]
Stack Operation SS[SS] NONE SP[SP]
Variable (except DS0[DS] PS[CS], DS1[ES], Effective
following) SS[SS] Address
String Source DS0[DS] PS[CS], DS1[ES], IX[SI]
SS[SS]
String Destination DS1[ES] NONE IY[DI]
BP[BP] Used As SS[SS] PS[CS], DS0[DS], Effective
Base Register DS1[ES] Address
BW[BX] Used As DS0[DS] PS[CS], DS1[ES], Effective
Base Register SS[SS] Address
Prefetch Pointer
PFP [IP]
The prefetch pointer PFP [IP] is a 16-bit binary counter that
maintains the offset of the next instruction to be fetched into the
instruction queue. The BCU fetches a program instruction based
on the segment value in the PS [CS] register and the offset in the
PFP [IP].
5-9