Electronics/Computer Projects

Well, this post contains both good news and bad news: Good News part 1. I spent the later half of yesterday wiring up the arduino to the EEPROM board proper. I then began to check basic functionality such as proper voltages, proper and state of the EEPROM control lines. Everything checked out, so I decided to test with an NVRAM that has an identical pinout. I encountered a few errors in the software in this process. The controller was not allowing the device to complete a read or write cycle before moving on to the next byte, fixed by adding a 1ms delay between pulling the read or write lines low, and pulling them back up. I accidentally left out a = in the test part of some if statements, so it would read as 'if(Error=1)' instead of 'if(Error==1)'. This caused the send/receive portions of the write and dump routines to fail out, thinking the Xmodem packet was being improperly received or sent. The first 128 bytes of the NVRAM was being rewritten with data from the

I have decided to revisit my earlier plan of making an EEPROM programmer with as few I/O pins required as possible. I have decided to abandon that requirement in favor of making something functionally complete with a minimum of software development required. I'm using an Arduino Mega as the programming controller, with the sole reason being the large amount of I/O pins available. Rather than reflashing the controller every time an EEPROM needs to be rewritten to hold a new program, I've implemented a method to send the desired program over a serial connection, and program the EEPROM in 128-byte chunks. This is done via the Xmodem protocol, which allows for a pause between packets to allow time for programming 128 bytes at a time, before requesting the next packet. Due to the variant of EEPROM I have, a 12V level signal needs to be applied to the /OE pin in order to enable a full chip erase. This 12V line will be handled by an opto-coupler, and a momentary pushbutton acting

So I've started work on the BIOS-ROM for the Z80-based Zephyr computer in preparation for use with BP-DOS, and I needed to decide between SCSI or IDE for a storage disk. The SCSI disk I have would be ideal on the hardware level, since both commands and data are 8-bit (with hardware generated/checked parity), plus it would make for a nice auditory experience being a full-height 5.25" disk. However, an issue arose when reading through the commands section of the SCSI standard, there are several different bus phases, and the flow path can be quite confusing at times. I'm sure given time it could be done, but I'm interested in getting the Zephyr computer running in a reasonable time frame. Instead, I have opted for using one or two IDE disks, for simplicity of the bus and command-set. Data transfers are done on 16-bit words, so a data read/write takes two input/output cycles from the CPU, and the ordering of which byte of the word will vary between reads and writes. On

I've decided to write a small and very limited operating system called BluePrint-DOS (BP-DOS) for my computers, with the goal being to require a minimal amount of hardware, and to more easily facilitate running programs, by loading them from a block-storage device than burning an EEPROM every time a new program is to be tested/run. The hardware requirements will be: 32KB of RAM, to hold both OS routines and the running program A free-running timer to facilitate CPU 'sleeping' when no action is being done. A block storage device to store OS and program files. User I/O, for hopefully obvious reasons. The function of the OS itself will be to: Load, run, and return from user programs. Provide file system routines for reading/writing files to the selected block device. Lower level functions will be stored in ROM, and these include: Block-storage sector read/write routines. User input hardware routines. Timer interrupt service routine. Display hardware routin

So, I'll be needing an EEPROM programmer in order to actually provide some startup software for my Z80 computer. I intend to make one using a set of shift registers, and a couple optoisolators, so that I can use any microcontroller with 8 I/O pins (7 output, 1 input), assigned as follows: Input: 1 = Data Read Output: 1 = Address/Data Write 2 = Shift 3 = ~WE 4 = ~CE 5 = ~OE 6 = ERASE/VPP (EEPROM/EPROM) 7 = Read Data The design will be as such that any microcontroller that uses either 3.3V, or 5V I/O can safely operate it. An interesting design requirement involves needing to have either 3.3/5V or 12V sent to the ~OE pin of an EEPROM, as the 5V signal is used to read from it, but the 12V is required in order to erase it. A possible solution will be to use a diode to prevent the 12V signal from feeding back to the microcontroller, and an optoisolator to gate the 12V to the same pin during an erase cycle. To obtain the 5V and 12V power rails, I will use a simple regulat

This blog is intended to showcase my electronics and computer projects, as well as educating about related concepts. I currently have an ongoing project consisting of an 8-bit computer I call Zephyr (because I'm bad at coming up with names). Details as follow: CPU: Zilog Z80 rated to 10MHz (Currently running at 625KHz) Memory: 8KB of ROM, 32KB of RAM with room for expansion I/O: Serial Currently it doesn't do anything since I need to create an EEPROM programmer, which I plan to make using shift registers and a controller of some variety. I also have plans to create another 8-bit computer project called CosNaut (Again, bad at names) using an RCA 1802 'COSMAC' CPU, though anything else is not set in stone. Will post updates as necessary.