Mass storage
Forth without mass storage (blocks, screens) is a not complete. A SD-Card interface could be a reasonable solution but this is an overkill for a small Forth system.
EEPROM Serial Communication
Serial Peripheral Interface SPI, MC is the SPI master, the host is the slave.
e.g.
AT25M02 SPI EEPROM 2Mbit (256 KiB, $3) or
25LC512 (64 KiB, $1.50). DIL8 Package. 256 KiB seems very small for today's standards where storage is quantified in GiB, but I think it's more than enough for a small Forth system.
CLK MC ->- host
MOSI MC ->- host
MISO MC -<- host
SS MC ->- host or other peripherals (optional)
A high-to-low transition on the CS pin is required to start an operation and a
low-to-high transition is required to end an operation.
Invalid Opcode: If an invalid opcode is received, no data will be shifted into
AT25M02 and the Serial Data
Output (SO) pin will remain in a high impedance state until the falling edge of CS is detected again. This will
reinitialize the serial communication.
25LC512 Instruction Set
Name |
Format |
Description |
READ |
0000 0011 |
Read data from memory array beginning at selected address |
WRITE |
0000 0010 |
Write data to memory array beginning at selected address |
WREN |
0000 0110 |
Set the write enable latch (enable write operations) |
WRDI |
0000 0100 |
Reset the write enable latch (disable write operations) |
RDSR |
0000 0101 |
Read STATUS register |
WRSR |
0000 0001 |
Write STATUS register |
PE |
0100 0010 |
Page Erase – erase one page in memory array |
SE |
1101 1000 |
Sector Erase – erase one sector in memory array |
CE |
1100 0111 |
Chip Erase – erase all sectors in memory array |
RDID |
1010 1011 |
Release from Deep power-down and read electronic signature |
DPD |
1011 1001 |
Deep Power-Dow |
AT25M02 Instruction Set
Name |
Format |
Description |
READ |
0000 0011 |
Read from Memory Array |
WRITE |
0000 0010 |
Write to Memory Array |
WREN |
0000 0110 |
Set Write Enable Latch (WEL) |
WRDI |
0000 0100 |
Reset Write Enable Latch (WEL) |
RDSR |
0000 0101 |
Read Status Register (SR) |
WRSR |
0000 0001 |
Write Status Register (SR) |
LPWP |
0000 1000 |
Low Power Write Poll |
Serial EEPROM Connected to Centronics Connector (Switches and LEDs)
Sharing the LED and Switch port, you loose two LEDs and one switch. Conflict with the bootstrap loader, some sort of disable EEPROM needed e.g. switch or jumper.
SPI |
MC (Master) |
AT25xxx (Slave) |
Interface |
|
" |
3 WP |
+5V |
|
" |
7 HOLD |
+5V |
|
21 GND |
4 GND |
GND |
CS |
? O5 LED5 |
1 CS |
Pullup 10 k, switch to GND |
CLK |
J2.10 O6 LED6 |
6 SCK |
direct |
MOSI |
J2.11 O7 LED7 |
5 SI |
direct |
MISO |
J2.9 IN7 SWITCH7 |
2 SO |
direct |
|
P4.3 VDD |
8 VCC |
+5V |
Raspberry Pi can emulate SPI EEPROM. On
RaspiElf the switches/LEDs are already connected to Raspi's GPIOs. No need for additional hardware. But I have to write an SPI server for the Raspberry Pi.
Serial EEPROM patched on MC PCB
SPI Mode 0, data is always latched in on the rising edge of SCK and always output on the falling edge of SCK.
Kermit/ZModem
What about using KERMIT or ZMODEM protocol for the file transfer and use
the file system on the host? No need to add additional hardware (SD-card
is anyway to modern
You could use an old CP/M or even a PDP11 as host. The C-Kermit Local Server mode, e.g. MC can read/write the blocks as files
block.0
,
block.2
,
block.255
.
https://github.com/utoh/pygmy-forth/blob/master/extras/kermit/pfkerm.doc