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Phillip Stevens edited this page Aug 22, 2023 · 11 revisions

RC2014 MS BASIC v4.7, (C) 1978 Microsoft

This standard MS Basic ROM works with the Mini, Mini II, Micro, and Classic versions of the RC2014, with 32kB of RAM.

Alternate versions of the MS Basic ROM v4.7 supporting the RC2014 64kB RAM Module, and the Am9511A APU Module can be found here.

The NASCOM MS Basic User Manual is available here and elsewhere. The NASCOM screen specific instructions have been removed or replaced by VT100 equivalents.

This MS Basic ROM provides both an Intel HEX uploading function HLOAD, and an RST, INT0, and NMI RAM Jump Table starting at 0x8000. The Intel HEX upload function allows you to upload Assembly or compiled C programs, and then run them as described below. The RAM Jump Table allows reconfiguration of important jump instruction destinations, that would otherwise be fixed by their location in ROM.

The goal of the Intel HEX uploading function addition to standard MS Basic is to load an arbitrary program in Intel HEX format into an arbitrary location in the z80 address space, and allow you to start and use your program from MS Basic. Your program can be created in assembler, or in C, provided the code is available in Intel HEX format.

Additional BASIC statements MEEK I,J and MOKE I have been added, which allow convenient editing of small assembly programs from the BASIC command line. The WIDTH I,J statement has been extended to support setting the comma column screen width.

Start up debugging

The RC2014 serial interface is configured to use 115200 baud with 8n2. Inter-character delays are not required, provided the terminal emulator supports hardware flow control.

On initial power up, or on RESET, there is a BEL (0x07) character output from the serial port. If you have a terminal supporting BEL you will hear it. Otherwise check that 0x07 is being transmitted by looking at the characters received. If you do not hear or see BEL then it is likely that your terminal emulator is not properly configured, or that the RC2014 Mini, or RC2014 Classic Z80 Module, ACIA Serial Module, or ROM Module has a fault.

Immediately following a RAM Module sanity check will ensure that the serial port can be fully initialised, and then BASIC loaded. If the RAM Module sanity check fails a character will be continually output, which can be used to infer what is causing the problem. Seeing either 0xFF or 0x00 would infer that there is no RAM in the required location. Other values infer that there is a problem with the address lines or data lines.

Otherwise, by entering C or W on your keyboard, you should see this start up message on your terminal the BASIC prompt Ok.

RC2014 - MS Basic Loader
z88dk - feilipu

Cold | Warm start (C|W) ? C

Memory top?
Z80 BASIC Ver 4.7c
Copyright (C) 1978 by Microsoft
31948 Bytes free

Ok

Uploading BASIC Programs

Programs can be easily uploaded to BASIC using either the terminal emulator raw file upload capability, or using Linux cat < input_file.bas > /dev/ttyUSB0 for example. Provided that your terminal emulator and USB-Serial (FTDI) device support hardware flow control there is no need to use inter-character or inter-line delays. This is also true for Linux cat. If the program upload (transcription) doesn't complete properly because flow control is not working effectively, just clear the partial upload using NEW and repeat the upload with the terminal configured with a small inter-line delay.

Assembly (or compiled C) Program Usage

Please refer to Appendix D of the NASCOM 2 MS Basic Manual for information on loading and running Assembly Language programs.

The MEEK I,J and MOKE I statements can be used to hand edit assembly programs, where I is the address of interest as a signed integer, and J is the number of 16 byte blocks to display. MOKE byte entry can be skipped with carriage return, and the function is exited with CTRL C. For manually entered assembly programs the user program address needs to be manually entered into the USRLOC address 0x8204 using DOKE.

Address entry can also be converted from HEX to signed integer using the & HEX prefix, i.e. in MOKE &9000 0x9000 is converted to −28672 by use of the & prefix which is simpler than calculating this signed 16 bit integer by hand, and MEEK &9000,&10 will tabulate and print 16 blocks of 16 bytes of memory from memory address 0x9000.

Usage Example

Using HLOAD for uploading compiled and assembled programs.

  1. Select the preferred origin .ORG for your arbitrary program, and assemble a HEX file using your preferred assembler, or compile a C program using z88dk. One option is to use the Zen assembler for BASIC. For the RC2014 32kB suitable code origins commence from 0x8400, and the default origin for z88dk RC2014 is 0x9000 (which allows some remaining space for a small BASIC program).

  2. At the BASIC interpreter type HLOAD, then the command will initiate and look for your program's Intel HEX formatted information on the serial interface.

  3. Using a serial terminal, upload the HEX file for your arbitrary program that you prepared in Step 1, using the Linux cat utility or similar. If desired the python slowprint.py program can also be used for this purpose. python slowprint.py > /dev/ttyUSB0 < myprogram.hex or cat > /dev/ttyUSB0 < myprogram.hex. The RC2014 serial interface can absorb full rate uploads, and supports hardware flow control, so using slowprint.py is an unnecessary precaution.

  4. Once the final line of the HEX code is read into memory, HLOAD will return to MS Basic with ok. The HLOAD statement automatically configures the BASIC USRLOC to be the first address contained in the Intel HEX file.

  5. Start your program by typing PRINT USR(0), or ? USR(0), or other variant if you have an input parameter to pass to your program.

The HLOAD command can be exited without uploading a valid HEX file by typing : followed by CR CR CR CR CR CR or any other characters.

The top of BASIC memory can be readjusted by using the RESET statement, when required. RESET is functionally equivalent to a restart.

USR Jump Address & Parameter Access

For the RC2014 with 32k MS Basic the USRLOC loaded user program address is located at 0x8204.

Your assembly program can receive a 16 bit parameter passed in from the function by calling DEINT at 0x0AE1. The parameter is stored in register pair DE.

When your assembly program is finished it can return a 16 bit parameter stored in A (MSB) and B (LSB) by jumping to ABPASS which is located at 0x1274.

Note that these address of these functions can also be read from 0x024B for DEINT and 0x024D for ABPASS, as noted in the NASCOM Basic Manual.

                                ; from Nascom Basic Symbol Tables
DEINT           .EQU    $0AE1   ; Function DEINT to get USR(x) into DE registers
ABPASS          .EQU    $1274   ; Function ABPASS to put output into AB register for return


                .ORG    9000H   ; your code origin, for example
                CALL    DEINT   ; get the USR(x) argument in DE

                                ; your code here

                JP      ABPASS  ; return the 16 bit value to USR(x). Note JP not CALL

RST locations

For convenience for assembly language programming using this MS Basic ROM, the serial Tx and Rx routines are reachable from your program by calling the RST instructions from your assembly program.

  • Tx: RST 08 expects a byte to transmit in the a register. Preserves HL, DE, and BC, and all alternate registers.
  • Rx: RST 10 returns a received byte in the a register, and will block (loop) until it has a byte to return. Preserves HL, DE, and BC, and all alternate registers.
  • Rx Check: RST 18 will immediately return the number of bytes in the Rx buffer (0 if buffer empty) in the a register. Preserves HL, DE, and BC, and all alternate registers.
  • Unused: RST 20, RST 28, RST 30 are available to the user.
  • INT: RST 38 is used by the ACIA 68B50 Serial Device through the IM1 INT location.
  • NMI: NMI is unused and is available to the user.

All RST nn targets can be rewritten in a JP table originating at 0x8000 in RAM. This allows the use of debugging tools and reorganising the efficient RST instructions as needed. Check the source to see the address of each RST xx. By default, if not defined, the unused RST nn targets return a ?UF Error code. For more information on configuring and using the RST nn targets refer to the example in the Wiki.

Notes

Note that your C or assembly program and the USRLOC address setting will remain in place through a RC2014 Warm Reset, provided you prevent BASIC from initialising the RAM locations you have used. Also, you can reload your assembly program to the same RAM location through multiple Warm Resets, without reprogramming the USRLOC jump.

Any BASIC programs loaded will also remain in place during a Warm Reset.

Issuing the RESET keyword will clear the RC2014 RAM, and provide an option to return the original memory size. RESET is functionally equivalent to a restart.

The standard MS Basic WIDTH statement has been extended to support setting the comma column screen width using WIDTH I,J where I is the screen width, and J is the comma column screen width.

Serial Interface

The RC2014 ACIA 6850B serial interface is configured to use 115200 baud with 8n2. The interface supports interrupt driven serial I/O, and the receive interface has a 255 byte software buffer, together with optimised buffer management supporting the 6850B ACIA receive double buffer. Receive hardware RTS flow control is provided. The ACIA transmit interface is also buffered, with direct cut-through when the 63 byte software transmit buffer is empty, to ensure that the CPU is not held in wait state during serial transmission.

Credits

Derived from the work of @fbergama and @foxweb at RC2014. https://github.com/RC2014Z80/RC2014/tree/master/BASIC-Programs/hexload

Derived from the work of Grant Searle. The HEX number handling updates to the original BASIC within this file are copyright (C) Grant Searle http://searle.wales/

Copyright

NASCOM ROM BASIC Ver 4.7, (C) 1978 Microsoft Scanned from source published in 80-BUS NEWS from Vol 2, Issue 3 (May-June 1983) to Vol 3, Issue 3 (May-June 1984). Adapted for the freeware Zilog Macro Assembler 2.10 to produce the original ROM code (checksum A934H). PA http://www.nascomhomepage.com/

The rework to support MS Basic MEEK, MOKE, HLOAD, RESET, WIDTH, and the 8085 and Z80 instruction tuning are copyright (C) 2021-23 Phillip Stevens. This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

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