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link to nchrs notes, small formatting

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@ -105,6 +105,9 @@ we'll come back to postfix notation and the stack very soon!
one of the perks of programming a computer at a low-level of abstraction, as we will be doing with uxn, is that we have to know and be aware of its internal workings.
for this section of the tutorial, i recommend you to follow along with the great illustrations and notes by Rostiger:
=> https://nchrs.xyz/uxn_notes.html nchrs: uxn notes
## 8-bits and hexadecimal
binary words of 8-bits, also known as bytes, are the basic elements of data encoding and manipulation in uxn.
@ -117,26 +120,26 @@ a byte needs two hexadecimal digits (nibbles) to be expressed, and a short needs
## the uxn cpu
it is said that the uxn cpu is a beet, capable of performing 32 different instructions with three different mode flags.
it is said that the uxn cpu is a beet, capable of performing 36 different instructions with three different mode flags.
each instruction along with its mode flags can be encoded in a single word of 8-bits.
all of these instructions operate with elements in the stack, either to get from it their operands and/or to push down onto it their results.
we'll be covering these instructions slowly over this tutorial.
we'll be covering these instructions very calmly over this tutorial.
## memory
memory in a uxn computer consists in four separate spaces:
* main memory, with 65536 bytes
* i/o memory, with 256 bytes divided in 16 sections (or devices) of 16 bytes each
* working stack, with 256 bytes
* return stack, with 256 bytes
* a main memory, with 65536 bytes.
* i/o memory, with 256 bytes divided in 16 sections (or devices) of 16 bytes each.
* a working stack, with 256 bytes.
* a return stack, with 256 bytes.
each byte in the main memory has an address of 16-bits (2 bytes) in size, while each byte in the i/o memory has an address of 8-bits (1 byte) in size. both of them can be accessed randomly.
the first 256 bytes of the main memory constitute a section called the zero page. this section can be addressed by 8-bits (1 byte), and it is meant for data storage during runtime of the machine.
the first 256 bytes of the main memory constitute a section called the zero-page. this section can be addressed by 8-bits (1 byte), and it is meant for data storage during the runtime of the machine.
there are different instructions for interacting with each of these memory spaces.