From 4786ad87d6f2c5415a88ad4c62a372244b0dd609 Mon Sep 17 00:00:00 2001
From: Roman Boykov <romychs@gmail.com>
Date: Fri, 16 Oct 2026 12:02:04 +0300
Subject: [PATCH] Documentation fixes

---
 README.md   |  5 +++--
 ioports.inc | 15 ++++++++++++---
 orion.asm   |  2 +-
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index b79bb2e..cdc6856 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,8 @@
 # MSX Basic for Orion-128 computer
 
-Source codes of MSX Basic-80, for Orion-128 computer (i8080 or Z80 CPU, 64k RAM).
-Application was loading from the tape at address 0x0000.
+Source codes of MSX Basic-80, for Orion-128 computer with ORDOS operating system (i8080 or Z80 CPU, 128k RAM).
+
+Application was loading from the RAM-drive at RAM address 0x0000.
 
 I tried to preserve the original label names exactly as they appear in the source code published by Microsoft.
 
diff --git a/ioports.inc b/ioports.inc
index 20bba0b..2d69f4e 100644
--- a/ioports.inc
+++ b/ioports.inc
@@ -7,12 +7,21 @@
 
 
 ; System port mapped to RAM address.
+; Matrix keyboard rows 0..7
 PORT_F400_KBD  EQU 0xf400
 
 ; System port mapped to RAM address.
+; Matrix keyboard columns 0..7
 PORT_F401_KBD  EQU 0xf401
 
 ; System port mapped to RAM address.
+;   bit 0 - Tape Output
+;   bit 2 - Output "RUS/LAT" LED indicator
+;   bit 3 - Output "TapeIn" LED indicator
+;   bit 4 - Tape Input
+;   bit 5 - Input "Ctrl" keyboard key
+;   bit 6 - Input "Shift" keyboard key
+;   bit 7 - Input "RUS/LAT" keyboard key
 PORT_F402_KBD  EQU 0xf402
 
 ; System port mapped to RAM address.
@@ -26,12 +35,12 @@ PORT_F600_USR2 EQU 0xf600
 PORT_F601_USR2 EQU 0xf601
 
 ; System port mapped to RAM address.
+; LPT Control port:
+;   bit 3 - input BUSY sygnal
+;   bit 7 - output #STROBE sygnal
 PORT_F602_USR2 EQU 0xf602
 
 ; System port mapped to RAM address.
-; LPT Control port
-; bit 7 - output /STROBE sygnal
-; bit 3 - input BUSY sygnal
 PORT_F603_USR2 EQU 0xf603
 
 ; System port mapped to RAM address.
diff --git a/orion.asm b/orion.asm
index 712e739..43db139 100644
--- a/orion.asm
+++ b/orion.asm
@@ -2833,7 +2833,7 @@ OR_PACK_FBCOLR:
 
 ; --------------------------------------------------
 OR_SCRN_CELL_ADDR:
-    DEC   H
+    DEC   H                                         ; 384 × 256
     DEC   L
     LD    E, H
     LD    H, 0x00