Hardware

Hardware Overview and Comparison

	F256Jr	F256K
CPU	WDC W65C02S WDC W65C816S Foenix FNX6809	WDC W65C02S WDC W65C816S Foenix FNX6809
RAM	512 KB Optional 256K RAM expansion module available	512 KB Optional 256K RAM expansion module available
Flash	512 KB Optional 256K Flash Modules	512 KB Optional 256K Flash Modules
Graphic Chip	TinyVicky	TinyVicky
Audio	2 x PSG (SN76489) 2 x SID socket	2 x PSG 2 x SID hardware emulation on board OPL3 CODEC
Connections	1 x DVI (digital & analog) 1 x PS2 (Mouse / External Keyboard) 1 x Commodore syle IEC Port 1 x Headphone 3.5 1 x RCA Line Out 2 x Serial Port Pin-Header 1 x Mini-USB Debug Port 1 x Power 12V / 2A, 2,5mm Barrel Connector 1 x SD Card Slot 2 x Joystick Atari style Pin-Header 1 x PIN-Header onboard for SNES/NES Joystick Connector Box 1 x Memory Expansion Slot (on Top) 1 x JTAG Port for system updates (on bottom) 1 x Wifi Module ESP32 Feather (internal) 1 x Real Time Clock Battery CR2032 (internal)	1 x DVI (digital & analog) 1 x PS2 (Mouse / External Keyboard) 1 x Commodore syle IEC Port 1 x Headphone 3.5 1 x RCA Line Out 1 x Serial Port DB9M / 1 x Serial Pin Header 1 x Mini-USB Debug Port 1 x Power 12V / 2A, 2,5mm Barrel Connector 1 x SD Card Slot 2 x Joystick Atari style DB9 Connector 1 x Mini-DIN9 for SNES/NES Joystick Connector Box 1 x Memory Expansion Slot (on Top) 1 x JTAG Port for system updates (on bottom) 1 x Wifi Module ESP32 Feather (internal) 1 x Real Time Clock Battery CR2032 (internal)

Hardware Details

CPU

The basic setup of all F256 is the Western Design Center 65C02, a slightly enhanced CMOS version of the very popular 6502 CPUs. The main difference to the 6502 in the 1970s and 1980s is the faster clock speed and the lower power consumption.

The 65C02 can also be replaced with a 65816 as a drop in replacement. Note, however, that while the 65c02 includes the additional Rockwell instructions (BBS/BBR, RMB/SMB), the 65816 does NOT. Therefore, these instructions should be avoided to ensure compatibility with F256 machines using the 65816.

In the F256, the CPU is always clocked at 6,29 MHz (6,293,750 Hz to be exact, derived from 25.175 MHz / 4 as discussed on Discord).

Memory Expansion Slot

The memory expansion slot, located on the top right (above the keyboard), is intended primarily for Memory Expansion. It provides Address lines A0 - A17 (for addressing 256K), and active low Chip Select signal (CS_RAM) and Ouput Enable (OE) for the 256K Expansion address range $100000 - $13FFFF.

Foenix produce a 256K RAM Expansion cartridge, based on the CY7C1010DV33-10VXI, a high speed (10ns) 2Mbit (256K × 8) 3.3V Parallel Static RAM device.

The Expansion Slot itself, is based on a 36 pin PCI-Express x1 socket.

As the Expansion Slot also features pins for IRQ input, PHI2 clock output, and Reset (all signals which are unnecessary for a simple Memory interface), the Expansion Slot is also a candidate for other expansion purposes.

Utilising the Expension Slot (for your own purposes)

Warning: All signals on the Expansion Port are 3.3V logic level, therefore it is important that no voltage exceeding 3.3V is ever presented on any Expansion Port pin, or you risk damage to your F256!

If interfacing 5V TTL level devices to the Expansion Port, it is essential that level converters are used.

As an example, if directly interfacing to the Expansion Port pins with 5V logic, then you could use the SN74LVC8T245 bi-directional level translator, with the DIR input controlled by the Port's R/Wn signal (for the D0 - D7 bi-directional data bus), and the OEn input controlled by the Port's OEn signal. For the uni-directional Address and Control lines, the DIR input can be hardwired.

Note that the SN74LVC8T245 is designed so that the control pins (DIR and OE) are referenced to Vcca ('A' side voltage supplied). Therefore, a common practice would be to use side A for the internal (3.3V) side of the voltage translation, such that DIR and OE can be directly controlled by the Expansion Port's 3.3V level R/Wn and OEn pins. Side B (and Vccb) then being the 5V TTL level referenced (external facing) side.

As another example, if you were interfacing directly to a 3.3V peripheral chip (e.g. A W65C22 VIA powered by Vdd = 3.3V), but wanting to level translate to 5V TTL levels on the VIA's Port Pins, then an auto-direction level translator like the TI TXS010x series (TXS0108, TXS0104, TXS0101), might be more appropriate.

Note that on the TXS010x series the control pin (OE) is also referenced to Vcca ('A' side voltage supplied). With the TXS series, the 'A' side is actually limited to a 1.4V - 3.6V range, so is inherently the 3.3V internal side. Side 'B' is 1.65V - 5.5V, so is used for the external 5V TTL level referenced (external facing) side. So, if you're tying the active high OE pin of a TXS device (to permanently enable), it should be pulled to Vcca (not Vccb!).

Expansion Slot pin-out

Signal	Side B	Side A	Signal
A4	B1	A1	nRST
A3	B2	A2	A5
A2	B3	A3	A6
A1	B4	A4	A7
A0	B5	A5	A8
CS_RAMn	B6	A6	OEn
D0	B7	A7	D7
D1	B8	A8	D6
3V3	B9	A9	GND
GND	B10	A10	3V3
D2	B11	A11	D5
Key Notch
D3	B12	A12	D4
R/Wn	B13	A13	A9
A17	B14	A14	A10
A16	B15	A15	A11
A15	B16	A16	A12
A14	B17	A17	IRQn
A13	B18	A18	PHI2

Expansion Slot - Signal Descriptions

Signal	Description
A0 - A17	Address Bus output (for addressing $100000 - $13FFFF Expansion space)
D0 - D7	Data Bus (bi-directional)
RSTn	Reset output (active low)
CS_RAMn	Chip Select output for Address Range $100000 - $13FFFF (active low)
OEn	Output Enable output for a Read from Address Range $100000 - $13FFFF (active low)
3V3	3.3V Power output from the F256 (intended to power Expansion Interface only - Don't Exceed 500ma)
GND	Digital Ground reference
R/Wn	Read/Write ouput (Read = high / Write = low)
IRQn	Interrupt Request input - Internal pull-up and non-shared (compatible with open-drain or totem-pole driven)
PHI2	Phase 2 - Clock Output