FIN

Name

Fetch Indirect from ROM

Function

8 bits of immediate data are loaded into the register pair specified by RP.

Syntax

FIN RPp

Assembled

Binary

0010RRR0

Decimal

48, then incrementing by 2 until 62 (1st word)

Hexadecimal

0x30, then incrementing by 2 until 0x3E (1st word)

Symbolic

 ../../_images/fin-sym.png

Execution

1 word, 8-bit code but with an execution time of 21.6 \({\mu}\) sec

Side-effects

Not Applicable, unless RP0 is the designated target register pair, in which case, RP0 will contain the data at the memory location referenced by RP0 at the start of the instruction

Implemented

fin

Detailed Description

The contents of registers 0 and 1 are concatenated to form the lower 8 bits of a ROM or program RAM address. The upper 4 bits of the address are assumed equal to the upper 4 bits of the address at which the FIN instruction is located (that is, the address of the FIN instruction and the address referenced by registers 0 and 1 are on the same page). The 8 bits at the designated address are loaded into the register pair specified by RP. The 8 bits at the designated address are unaffected; the contents of registers 0 and 1 are unaffected unless RP = O.

The carry bit is not affected.

The target register pair is defined as part of the opcode as detailed below.

../../_images/fin.png

Example program

/ Example program
        org    ram
        fin    7p
        end

(Assume that address 0x25B contains the data 0x6E (spread over 2 words)).

If register 0 contains 0x5 and register 1 contains 0xB, when the FIN instruction is executed, the 8 bits located at hex address 0x25B will be loaded into register pair 7P. Thus register 14 will contain 0x6, and register 15 will contain 0xE.

Notes

If a FIN instruction is located in the last location of a page, the upper 4 bits of the designated address will be assumed equal to the upper 4 bits of the next page.

Thus if the instruction:

fin 7p

is located at decimal address 511 (0x1FF) and registers 0 and 1 contain 3 and 0xC, the 8 bits at address 0x23C (not 0x13C) will be loaded into registers 14 and 15.

This is dangerous programming practice and should be avoided whenever possible.