Z80 Computer CPU Card (USB Code Loader)

     Are you ready for some retro computer fun?  This Z80 CPU card allows for super fast experimentation without the delay or complexity that PROM/EPROM/EEPROM/NVRAM based systems introduce; no EPROM programmer (Or eraser for that matter!) required, just assemble your code, upload it immediately to the Z80 SRAM and run your program!

     The 1730 is a Z80 CPU card with a Z84C0008VEC processor and 64kB of SRAM.  This card uses a USB interface to upload code from a hex file into the SRAM and after upload, the SRAM can be copied into the USB controller's 64kB of Flash.  After each power cycle the Flash is copied into the SRAM and when the copy process is complete the bus is released, the Reset# signal is de-asserted and the Z80 is allowed to operate independently of the USB controller.  The Z80 clock can be supplied from a 8MHz crystal oscillator or by the USB controller in a frequency range of DC to 8MHz.

     With the USB controller the user also has the ability to do in-circuit-debug (ICD) of code: To set a breakpoint, just copy all the registers to RAM, execute a HALT instruction and then read out those registers (Or any number of bytes) with the Windows UI.  When ready to resume the UI can command a interrupt to restart the Z80.

     For added entertainment an LED signal watcher board can be plugged into the Z80 backplane or in-line with the CPU to examine every Z80 signal in real time.  Because the CMOS Z80 is fully static, it can be single stepped from the UI or push button on the CPU card or it can be clocked at any frequency from DC to 8MHz.

Features

• 3.0 inch wide by 2.5 inch high 4 layer PWB with 40 pin (2 x 20 x 0.1) edge mounted female connector to mate with the Z80 Backplane or user circuit
• All signals at the 40 pin connector are clearly labeled
• Reset button controls Z80 reset directly
• With the exception of the controller generated clock, all Z80 signals operate transparent to the USB controller unless a wait or reset is commanded via the UI:  This means the Z80 operates the same as if the USB controller was not there
• 8MHz Z84C0008VEC CMOS Z80 CPU: Static operation allows for single stepping
• Fixed 8MHz crystal oscillator or...
• Programmable clock from DC to 8MHz with the ability to halt and single step via serial link
• 64kB of SRAM that serves as both the ROM and RAM for the Z80 CPU that is up-loadable via USB in about 20S (About 3.3kB/Second).
• SRAM upload can be any number of bytes from 1 to 65536 bytes starting at any address (No wrap around allowed)
• SRAM can be executed by Z80 immediately after upload without copying to flash
• SRAM is copied to flash after upload is complete (if desired)
• SRAM download can be any number of bytes from 1 to 65536 bytes starting at any address...
• SRAM read from device generates a 32bit CRC:  Any single bit change in the SRAM results in at least 50% bit change in the CRC that can be used to inspect for ROM write violations, etc
• When the Z80 is halted, any portion of the SRAM can be downloaded over the serial link
• If user copies the Z80 registers to RAM prior to the halt instruction the UI can decode that space into a special set of UI registers when RAM is read, essentially creating an unlimited number of breakpoints for debugging
• 64kB of flash in the USB controller (10k write endurance) for non-volatile program storage
• Flash is copied to SRAM after each board power cycle in about 50mS
• LCD interface mapped to IO port addresses 0xFE (Control write) and 0xFF (Data read and write)
• Driver for LCD is available for download in the Z80 Library and  zDevStudio Projects (LCD Display code timing)
• All Z80 pins are connected to 40 pin dual row socket at bottom of the card
• Can be plugged into the Z80 Backplane for expansion and debugging
• Prototyping can be accomplished with the Backplane Proto Card that has pads on a 0.1 inch grid and space for up to four 40 pin DIPs or many more smaller packages
• Signals can be examined visually with the Signal Watcher or the Piggy Back Signal Watcher (Allows slot to be used by a plug in card on top of the viewer so the viewer doesn't take up the slot)
• Power supplied by USB Mini-B connection (With or without USB data interface) or from the 5V/2A regulator on the backplane (7 to 35V input)
• Free ZDevStudio assembler available: See Z80 resource page
• Sample code:  Z80 Library / zDevStudio Projects / zDevStudio Listing (Raw Debug data)
• zDevStudio uses the Pasmo compiler v0.6