figForth's Memory Map

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In The Beginning…

Around 1979, Forth was being promoted to home computer enthusiasts/hobbyists ¹ by the US-based Forth Interest Group (“FIG”)

Bear in mind, around the early 1980’s:

Home computers were VERY RUDAMENTARY and SLOW !!
Most were being clocked at 1MHz or so, and were B&W
No displays - An analogue TV ² had to be used via a RF-Modulator - Very low-res !
No software or apps - Just a Machine Code Monitor, program storage on Cassette Tape
No Tutorials with the computer – what you did get was for all practical purposes incomprehensible
There was NO INTERNET - that emerged in a very rudamentary form around 1995 ³
No computer books - No computer magazines, no tutorials

A detailed discussion of the “early days” is HERE and HERE…

So, How to Get Started ?

So, let’s just suppose you had a Nascom 1 home computer, like I did…

That was Zilog Z80-based and virtually identical code-wise to the Intel 8080, so you needed to obtain an 8080 FIG Forth Model (84 Pages) (FIG 1979) ⁴ and a FIG Forth Installation Manual (56 Pages) (FIG 1979)⁵ which at the time were both paper-based documents…

So you either had to send dollars ⁶ to FIG in the US and wait a few months or you joined FIG UK and sent a cheque to them instead.. And waited for the post…

Page 5 of the figForth model Installation Manual provides a memory map of the fig-Forth Model system ⁷

Image#1: The figForth Model Memory Map
Based upon (FIG 1979, p. 5), ignoring the other map on the right-hand side for the 6502

Looking back after 40 years I can see just how dreadful the those two fig documents actually were in terms of explanation and insight… The memory map is particularly bad in that respect… I have tried to address these issues in this website…

I was very lucky because I was introduced to figForth by my expert senior colleague at work…

The Zilog eZ80 Basics…

The “top-of-the-range” naked Zilog eZ80 has these resources internally:

(a) 8k General Purpose RAM

(A) 00-FFFF = Top of 64k Memory Range

(1) 00-FF77 = SP0 (Parameter Stack Pointer)

(2) 00-E300 = INITR0 (Return Stack Pointer)

(3) 00-E100 = UP0 (User Pointer)

(B) 00-E000 = INITTIB (Terminal Input Buffer

(b) 8k EMAC DMA RAM

(C) 00-DFFF = Top of 8k EMAC DMA RAM

(3) 00-C800 = Boundary in 8k EMAC DMA RAM

(D) 00-C000 = Bottom of 8k EMAC DMA RAM

(c) 48k of internal Flash ROM

(E) 00-BFFF = Top of 48k internal Flash ROM

(6) 00-758B = End of Forth Dictionary (in ROM)

(5) 00-0115 = Start of Forth Dictionary (in ROM)

(d) So what is going on here?

(F) 00-0000 = Bottom of 48k internal Flash ROM & of 64k Memory Range

Http://ez80.baremetal.engineer/eZ80.CPU.User.Manual-UM0077.pdf

Http://ez80.baremetal.engineer/eZ80F91.ASSP.Product.Spec-PS0270.pdf

Http://ez80.baremetal.engineer/eZ80F91.MCU.Product.Spec-PS0192.pdf

References:

FIG, 1979. Forth Model: fig-forth_8080_ver_11. Forth Interest Group [online]. Available from: Http://figforth.org.uk/library/fig-forth_8080_ver_11.pdf.

FIG, 1979. Forth Model: figForth Installation Manual. Forth Interest Group [online]. Available from: Http://figforth.org.uk/library/fig-FORTH_Manuals_May79.pdf.

And home computers were an unheard of and a very nerdy pastime… They were kits originally… ↩
Colour TVs were still very expensive ↩
Phone lines, slow modems… ↩
This was the “latest” and last fig 8080 model, updated so as to run on a CPM-based Machine… ↩
With a “sample” memory-map on page 5… ↩
At that time very few had a credit card, (debit cards did not exist yet) so you had to attend your bank and buy a banker’s draft in dollars, having added what you thought the postage from the US might be… Fun! Fun! ↩
And in my opinion, a very uninformative and uninspiring diagram… ↩