Getting started

Install the core first: Chapter 5 of the official MEGA65 User's Guide explains how to flash a .cor file into a core slot using MEGAFLASH. Use an available slot and do not overwrite the factory core in slot 0.

Start an alternate core: Switch the MEGA65 off, hold down NO SCROLL, then switch it on again. When the core selection appears, release the key and press the number of the slot containing the Nascom 2 core—without CTRL. CTRL plus a slot number opens the flashing editor instead.

NAS-SYS 3 appears after startup. The machine is ready to use immediately.

Basics

Display memory from $1000 with T1000. Enter modify mode with M1000, then type, for example, 23, 42, FF and finally .. Use T1000 again to check the result.

Loading a program from SD card

1. Put a NAS or CAS file in the /NASCOM2 directory on the SD card.
2. Open the browser with F11, select the file and confirm with Enter.
3. Note the displayed start address, close the browser with F11, and run the program, for example with E1000.

Start Microsoft BASIC after a reset with J. Press Enter at the memory-size prompt. MONITOR returns to NAS-SYS.

Important function keys

FDD and NAS-DOS

Press F13 twice to open the second configuration page and enable FDD / NAS-DOS. This maps NAS-DOS to $D000–$DFFF. In the file browser, Enter mounts a 640 KiB DSK image as logical drives 0/1, while Shift+Enter uses drives 2/3. Recognised images are marked [CP/M] or [NASSYS].

Activate the ROM from NAS-SYS with E D000. ]D then lists the first disk side; ]D1 through ]D3 select the other logical drives. ]E:NAME: loads and runs a program. Every NAS-DOS disk command begins with ].

CP/M 2.2

Enable CP/M-MODUS on the second F13 page. FDD support and the required RAM regions are enabled automatically. Mount CPM22.DSK as drives 0/1 in the F11 browser and reset the machine. DIR and STAT are useful first tests at the A> prompt.

The system disk includes FORMAT, SYSGEN, DISKCOPY, TIME, AVCTEST, AVCDIAG, AVCDEMO, KERMIT, assemblers, a debugger and the TE editor. CPMNET.DSK adds PING.COM, TELNET.COM and FTP.COM for the Ethernet interface.

Sound

Version 1.9 adds an AY-3-8910-compatible sound generator with three tone channels, noise and an envelope generator. It outputs 48 kHz, 16-bit audio simultaneously over HDMI and the 3.5 mm jack; VGA carries no audio.

Start BASIC with J and test channel A:

10 REM AY CHANNEL A - ABOUT 1 KHZ
20 OUT 8,0:OUT 9,125
30 OUT 8,1:OUT 9,0
40 OUT 8,7:OUT 9,62
50 OUT 8,8:OUT 9,15

After RUN, the tone continues because the AY registers retain their values. Stop it with OUT 8,8:OUT 9,0. Port 8 selects an AY register; port 9 reads or writes its value.

Joysticks

The two digital MEGA65 joystick sockets are connected to AY I/O registers 14 and 15. Up, Down, Left, Right and Fire are supported; all signals are active low. Load JOYTEST.NAS, run it with E 1000, and test both sockets live. Analogue paddle inputs are not currently exposed.

AVC graphics

Enable AVC on the second F13 page. The emulated Lucas Logic AVC Model B offers 392 × 256 pixels in eight colours or 784 × 256 monochrome. With CP/M it is automatically used as a 96 × 24 character terminal. AVCTEST, AVCDEMO and AVCDIAG on CPM22.DSK demonstrate and test the graphics system.

To use the original G48.NAS BASIC extension, leave CP/M off and set $B000–$B7FF, $B800–$BFFF and $C000–$CFFF to RAM on the second configuration page.

Real-time clock

Load RTC.NAS and run it with E 1000. The core uses either the onboard RTC or a valid external DS3231 on the Grove connector automatically. When both are available, the external clock takes priority; no manual selection is required.

Networking

Ethernet is available on R3/R3A and R6 and is initially disabled. Press F13 three times, enable networking on NETWORK 3/3, and choose either static IPv4 settings or DHCP. The page also displays the current link state.

The supplied NAS-SYS programs start as follows: PING.NAS at E 6000, TELNET.NAS at E 3000, FTP.NAS at E 5000, and CONTROL.NAS at E 4000. ARP, ping, DNS and outbound TCP connections are supported; IPv6, TLS and active-mode FTP are not.