It is built in CMOS technology with HCMOS chips, only the UVEPROM is NMOS.
Only technologies that were available in the 80s are used.
The Z80 CMOS CPU is clocked at 2 MHz (currently in the prototyping phase) but I'm planning to use frequencies up to 20 MHz (maximum frequency for CMOS). I'd like to have a go at overclocking, too. I've never overclocked my Z80 CPUs but I'll do so as part of my tests used to determine which CPUs are genuine and which are counterfeit. So far I've only carried out CMOS/NMOS tests but the CPU speed tests are due to take place next.
The reZet80 SENTINEL is equipped with 128 KiB of RAM and 4 KiB of ROM.
The 128 KiB RAM are divided into 4 banks of 32 KiB each but only the first two banks are addressed in R0 and R1.
128 I/O ports are provided, actually 8 ports of 16 addresses each.
4 ports are currently in use for the configuration and status registers, the keyboard and the LCD display.
One additional port will be used in R2 for the memory cartridge (NAND memcart).
The SENTINEL keyboard features a full keyboard (alphanumericals, 28 punctuation symbols and 7 special keys) with just 23 keys! More on this in my next post. It uses the 74C923 key encoder chip that supports key debouncing and interrupts. It triggers /NMI once a key is pressed.
An LCD display is used for visual output. All LCD displayes that use Hitachi's HD44780 dot matrix LCD controller or a compatible chip can be connected. In R0 only a 16x1 LCD module is supported but 16x2 and 40x1 modules will be added in R1 and even more in R2.
A configuration register (8-bit latch) is used for addressing the physical memory banks and to switch ROM out after boot.
The status register is an 8-bit buffer. It's used to control keyboard and memcart.
For the sake of completeness: inverter, oscillator and reset switch.
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