FT8U232A and FT8U245A

The first generation of fixed-function D2xx devices. The devices are:

• FT8U232AM: UART mode, 32-pin MQFP
• FT8U245AM: FIFO mode, 32-pin MQFP

Both devices look exactly the same from the software perspective, and in fact may or may not be the same silicon.

Features:

• is a full-speed USB 1.1 peripherial
• single channel D2xx device, hardwired to either UART or FIFO mode
  • no alternate bit modes
• 384-byte IN FIFO, 128-byte OUT FIFO
• 48MHz internal base clock, generated from 6MHz crystal
• 5V VCC supply (used for internal circuitry and business-end IO)
• separate AGND and AVCC supply for the clock multiplier
• internal 3.3V LDO
• required external support circuitry:
  • USB D+ pullup
  • power-on reset circuit
  • decoupling capacitor for internal LDO
  • RC timer for oscillator bootstrap
  • 6MHz crystal
  • optionally, a 93C46 64×16-bit EEPROM

The default VID:PID of the device is 0403:6001, unless configured otherwise by the EEPROM. The bcdDevice value is 0x0200.

Pinout

UART-mode IO pins have the following functions:

• TXD, RXD, RTS#, CTS#, DTR#, DSR#, DCD#, RI#: standard UART pins
• SLEEP#: device output, goes low when in USB suspend mode
• RXLED#, TXLED#: active-low LED outputs
• PWRCTL: device input, used to generate USB descriptors when EEPROM not present or not functional
  • 0: bus-powered
  • 1: self-powered
• TXDEN: device output, high while TXD is actively transmitting data; can be used as transmitter enable for RS485 transceivers
• USBEN: device output, high after the host configures the device

FIFO-mode IO pins have the following functions:

• D0-D7, TXE#, RXF#, RD#, WR: standard FIFO-mode pins
• EEREQ#: device input, requests access to EEPROM via data bus
• EEGNT#: device output, grants access to EEPROM via data bus

The semantics of EEREQ# and EEGNT# are unclear. They were removed from all subsequent devices.

TODO: wtf is this exactly

The EEPROM interface is 3-pin at the FTDI chip, while the EEPROM itself has a 4-pin interface. This is because the FTDI device uses a single tied data line. To connect the EEPROM, connect the FTDI EEDATA pin directly to the ROM's data input, and to the data output via a 2.2kΩ resistor.

EEPROM data format

• word 0x00: always 0
• word 0x01: idVendor (USB VID)
• word 0x02: idProduct (USB PID)
• word 0x03: bcdDevice (should be 0x200)
• word 0x04: USB config (goes straight to configuration descriptor)
  • bits 0-7: bmAttributes
    • bit 5: remote wakeup enabled
    • bit 6: self-powered
    • bit 7: always set to 1
  • bits 8-15: bMaxPower (max power in units of 2mA)
• words 0x05, 0x06: always 0
• word 0x07: manufacturer string pointer
• word 0x08: product description string pointer
• word 0x09: serial number string pointer
• words 0x0a..0x3f: string / user area
• word 0x3f: checksum

String pointers are formatted as follows:

• bits 0-6: pointer to descriptor within EEPROM (counted in bytes)
• bit 7: always set to 1
• bits 8-15: total length of descriptor in bytes

The string descriptors are stored in ROM with the descriptor header included, as follows:

• word 0: header
  • bits 0-7: total length of descriptor in bytes (includes header)
  • bits 8-15: descriptor type (always 3 — string)
• words 1 and up: string in UTF-16

The checksum can be computed as follows:

#![allow(unused)]
fn main() {
fn checksum(eeprom: &[u16; 0x40]) -> u16 {
    let mut res: u16 = 0xaaaa;
    for pos in 0..0x3f { // checksum word is NOT included — we're calculating it
        res ^= eeprom[pos];
        res = res.rotate_left(1);
    }
    res
}
}