PIC16F1704 — I2C Bridge Controller

Overview

The PIC16F1704 is a Microchip PIC microcontroller used in Antminer hash boards as an I2C bridge between the control board and the hash board's on-board peripherals. It sits on the main I2C bus (accessible from the control board via the signal connector) and provides bridged access to devices on the hash board's internal I2C bus, including temperature sensors (LM75A, NCT218) and the AT24C02 EEPROM.

The PIC acts as a protocol translator — it receives commands from the control board in a custom packet format, executes the corresponding I2C transactions on the internal bus, and returns the results. This architecture isolates the hash board's I2C bus from the control board's bus, preventing bus contention and allowing the PIC to manage timing-sensitive operations like voltage enable sequencing.

Specifications

I2C Address Behavior

When initializing communication with a hash board, always scan the full 0x20-0x27 range to locate the PIC. Do not hard-code a single address.

Communication Protocol

The PIC uses a custom packet-based protocol over I2C. The control board writes command packets to the PIC, waits for processing, then reads response packets.

Packet Format

Transmit (Control Board to PIC):

[55 AA] [LEN] [CMD] [param1] [param2] ... [CHECKSUM]

Receive (PIC to Control Board):

[LEN] [CMD] [STATUS] [data1] [data2] ... [CHECKSUM]

Field Descriptions

Checksum Calculation

The checksum covers all bytes from LEN to the last parameter byte (not including the sync bytes 55 AA):

def calculate_checksum(packet_without_sync):
    """Calculate PIC protocol checksum.

    packet_without_sync: bytes from LEN to last param (before checksum)
    """
    return sum(packet_without_sync) & 0xFF

# Example: CMD 0x15 (voltage enable), params [0x01, 0x00]
# Packet: [55 AA] [05] [15] [01] [00] [checksum]
# LEN=0x05, CMD=0x15, param1=0x01, param2=0x00
# Checksum = (0x05 + 0x15 + 0x01 + 0x00) & 0xFF = 0x1B

Command Reference

CMD 0x15 — Voltage Enable

Enables or disables the hash board voltage rails. This is the primary command used during initialization to power on the ASIC chips.

Transmit:

[55 AA] [05] [15] [enable] [0x00] [checksum]

Response:

[05] [15] [STATUS] [00] [checksum]

CMD 0x16 — Status Query

Reads the current status of the hash board (voltage state, fault flags).

Transmit:

[55 AA] [03] [16] [checksum]

Response:

[06] [16] [STATUS] [data1] [data2] [checksum]

Typical successful response: 06 16 01 00 00 1D

CMD 0x3C — Sensor Read

Reads data from a device on the hash board's internal I2C bus (temperature sensors, EEPROM).

Transmit:

[55 AA] [06] [3C] [target_addr] [nbytes] [register] [checksum]

Response:

[LEN] [3C] [STATUS] [byte1] [byte2] ... [checksum]

Example — Read temperature from LM75A at 0x48:

# TX: Read 2 bytes from register 0x00 at device 0x48
tx = bytes([0x55, 0xAA, 0x06, 0x3C, 0x48, 0x02, 0x00])
checksum = (0x06 + 0x3C + 0x48 + 0x02 + 0x00) & 0xFF  # = 0x8C
tx += bytes([checksum])

# Wait 50ms for PIC to complete the I2C transaction
time.sleep(0.05)

# RX: [07] [3C] [01] [temp_msb] [temp_lsb] [checksum]
# temp_msb=0x19, temp_lsb=0x00 → 25.0°C

CMD 0x3B — Sensor Read (Alternate)

An alternate sensor read command observed in sniffed I2C traffic.

Transmit:

[55 AA] [06] [3B] [target_addr] [0x00] [0x00] [checksum]

CMD 0x07 — Date Read

Reads the manufacturing date or calibration date stored in the PIC's internal memory.

Transmit:

[55 AA] [03] [07] [checksum]

CMD 0x06 — Hardware Info

Reads hardware version and configuration information.

Transmit:

[55 AA] [03] [06] [checksum]

Critical: Byte-by-Byte I2C Reads

Correct (byte-by-byte):

response = []
for i in range(expected_length):
    i2c_start()
    i2c_write(pic_addr << 1 | 1)  # Read mode
    byte = i2c_read_nack()         # Read one byte, NACK
    i2c_stop()
    response.append(byte)

Incorrect (multi-byte — will produce garbage):

# DO NOT DO THIS
i2c_start()
i2c_write(pic_addr << 1 | 1)
for i in range(expected_length - 1):
    response.append(i2c_read_ack())   # ACK to continue
response.append(i2c_read_nack())      # NACK to end
i2c_stop()

Initialization Sequence

The standard initialization sequence for communicating with a hash board via the PIC bridge:

Common Failure Modes

1. PIC Not Responding

Symptoms: No device found at any address in the 0x20-0x27 range during I2C scan. Hash board appears completely dead to the control board.

Causes:

• Failed PIC16F1704 IC
• Missing 3.3V power supply (check LDO regulator)
• Broken I2C SDA or SCL trace from the connector to the PIC
• PIC hung from a previous CMD 0x07 failure — try RST_N reset before assuming IC failure

Diagnosis:

1. Verify 3.3V at the PIC's VDD pin
2. Check SDA and SCL lines for stuck-LOW condition
3. Toggle RST_N (if accessible) to attempt a reset
4. If power and bus are good but PIC still does not respond, the IC has failed

2. Wrong I2C Address After Reset

Symptoms: PIC was at 0x20, after a reset it is now at 0x23. Software that hard-coded the previous address fails.

Causes: Normal behavior — the PIC address is not persistent across resets.

Fix: Always scan the full 0x20-0x27 range after any reset or power cycle. Never hard-code the PIC address.

3. Checksum Errors in Responses

Symptoms: Received data has incorrect checksums, or data appears garbled.

Causes:

• Multi-byte I2C reads (see the byte-by-byte requirement above)
• I2C bus noise from high-current switching on the board
• Marginal pull-up resistor values on the I2C bus

Fix: Ensure byte-by-byte reads. Add proper decoupling capacitors near the PIC. Verify I2C pull-up resistors are present and within the correct range (typically 4.7K to 10K ohms).

4. Sensor Reads Return Stale Data

Symptoms: Temperature readings do not change, or all sensors return the same value.

Causes:

• PIC is not completing the internal I2C transaction (internal bus issue)
• Target sensor has failed (PIC returns cached or default data)
• Insufficient wait time between CMD 0x3C and reading the response (need at least 50ms)

Fix: Increase the delay after CMD 0x3C to 100ms. Test sensors individually to identify which one is failing. Check the PIC's internal I2C bus (SDA/SCL between PIC and sensors) for continuity.

Replacement Notes

• The PIC16F1704 in SOIC-14 or TSSOP-14 is straightforward to desolder and replace with hot air
• The replacement PIC must be programmed with the correct firmware before installation — a blank PIC will not function as an I2C bridge
• PIC firmware is typically locked (code protection enabled) — you cannot read the firmware from a working PIC to copy it to a replacement
• Sources for programmed replacement PICs: donor boards (salvaged from other failed hash boards with different failures), aftermarket suppliers
• After installation, verify the PIC responds on I2C (scan 0x20-0x27) and can execute CMD 0x16 (status query)

Found In These Miners

• Antminer S19 — 1 per hash board
• Antminer S19 Pro — 1 per hash board
• Antminer S19 XP — 1 per hash board
• Antminer S21 — 1 per hash board
• Antminer S9 — 1 per hash board (older PIC variant)

Related Pages

• AT24C02 EEPROM (accessed via PIC bridge)
• LM75A Temperature Sensor (accessed via CMD 0x3C)
• NCT218 Temperature Sensor (accessed via CMD 0x3C)
• Temperature Sensors Overview
• Hashboard Connectors & Pinouts (I2C bus to PIC)
• UART, SPI & I2C Explained
• How Hash Boards Work