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/
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The HEX number handling updates to the original BASIC within this file are copyright (C) Grant Searle
You have permission to use this for NON COMMERCIAL USE ONLY. If you wish to use it elsewhere, please include an acknowledgement to myself.
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The rework to support MS Basic MEEK, MOKE, HLOAD, RESET, and the 8085 and Z80 instruction tuning are copyright (C) 2020-23 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/.
@feilipu, August 2020
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This ROM works with the PLUS versions of the RC2014, with 64k of RAM. This is the ROM to choose if you want fast I/O from a standard RC2014, together with the capability to upload C programs from within Basic.
ACIA 6850 interrupt driven serial I/O to run modified NASCOM Basic 4.7. Full input and output buffering with incoming data hardware handshaking. The handshake shows full 16 bytes before the buffer is totally filled, to allow run-on from the sender. Transmit and receive are interrupt driven, and are fast. The receive buffer is 255 bytes and the transmit buffer is 63 bytes. Use 115200 baud with 8n2.
Also, this ROM provides both Intel HEX loading functions and an RST, INT0, and NMI RAM Jump Table, starting at 0x2000. This allows you to upload Assembly or compiled C programs, and then run them as described below.
The goal of this extension 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 NASCOM 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 allow convenient editing of small assembly programs from the BASIC command line.
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 is not properly configured, or that the 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.
Please refer to Appendix D of the NASCOM 2 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 is exited with CTRL C. For hand assembly programs the user program address needs to be manually entered into the USRLOC address 0x2204 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 which is simpler than calculating this signed 16 bit integer by hand, and MEEK &2000,&10 will tabulate and print 16 blocks of 16 bytes of memory from memory address 0x2000.
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Select the preferred origin
.ORGfor your arbitrary program, and assemble a HEX file using your preferred assembler, or compile a C program using z88dk. For the RC2014 32kB suitable origins commence from0x2400, and the default origin for z88dk RC2014 is0x9000. -
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. -
Using a serial terminal, upload the HEX file for your arbitrary program that you prepared in Step 1, using the Linux
catutility or similar. If desired the pythonslowprint.pyprogram can also be used for this purpose.python slowprint.py > /dev/ttyUSB0 < myprogram.hexorcat > /dev/ttyUSB0 < myprogram.hex. The RC2014 interface can absorb full rate uploads, so usingslowprint.pyis an unnecessary precaution. -
Once the final line of the HEX code is read into memory,
HLOADwill return to NASCOM Basic withok. -
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 program can be exited without uploading a valid file by typing : followed by CR CR CR CR CR CR, or any other character.
The top of BASIC memory can be readjusted by using the RESET statement, when required. RESET is functionally equivalent to a cold start.
For the RC2014 with 56k Nascom Basic the USRLOC loaded user program address is located at 0x2204.
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 CALLFor convenience, because we can't easily change the ROM code interrupt routines this ROM provides for the RC2014, the ACIA serial Tx and Rx routines are reachable from your assembly program by calling the RST instructions from your program.
- Tx:
RST 08expects a byte to transmit in thearegister. - Rx:
RST 10returns a received byte in thearegister, and will block (loop) until it has a byte to return. - Rx Check:
RST 18will immediately return the number of bytes in the Rx buffer (0 if buffer empty) in thearegister. - Unused:
RST 20,RST 28,RST 30are available to the user. - INT:
RST 38is used by the ACIA 68B50 Serial Device through the IM1INTlocation. - NMI:
NMIis unused and is available to the user.
All RST nn targets can be rewritten in a JP table originating at 0x2000 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.
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 cold start.
The standard 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.
Derived from the work of @fbergama and @foxweb at RC2014.
https://github.com/RC2014Z80/RC2014/blob/master/ROMs/hexload/hexload.asm