PicoMite MMBasic BITSTREAM Command — User Manual

PicoMite MMBasic BITSTREAM Command — User Manual

BITSTREAM Command User Manual Overview The BITSTREAM command generates extremely accurate bit sequences on one or two GPIO pins. Each timing value in the array specifies the duration (in microseconds) before the pin state toggles. This enables precise generation of protocols like IR remote control signals, PS/2 keyboard/mouse communication, and other timing-critical waveforms. Syntax Single Pin Mode BITSTREAM pin, count, array() BITSTREAM pin, count, array(), mode Dual Pin Mode BITSTREAM pin1, count1, array1(), mode1, pin2, count2, array2() BITSTREAM pin1, count1, array1(), mode1, pin2, count2, array2(), mode2 BITSTREAM pin1, count1, array1(), mode1, pin2, count2, array2(), mode2, logic Parameters Parameter Description `pin`, `pin1`, `pin2` GPIO pin number(s) for the output. Can use GP notation (e.g., GP15) or physical pin numbers. `count`, `count1`, `count2` Number of timing values to use from the array (1 to 10000). `array()`, `array1()`, Numeric array containing timing values in microseconds. Each value specifies the time before the `array2()` next pin toggle. `mode`, `mode1`, `mode2` Output mode (optional, defaults to 0): **0** = Push-pull (driven high and low) **1** = Open-collector (driven low, high-impedance for high) `logic` Logic function for same-pin mode (optional, defaults to 0, only valid when pin1 = pin2): **0** = XOR (toggle on any event, original behavior) **1** = AND (output HIGH only when both logical states are HIGH) **2** = OR (output HIGH when either logical state is HIGH) Output Modes Push-Pull Mode (mode = 0) The pin is actively driven both high and low. This is the default mode and is suitable for most applications including: - IR LED driving (with appropriate current limiting) - Direct digital outputs - Single-ended signaling Open-Collector Mode (mode = 1) The pin is driven low for logic 0, and set to high-impedance (input with pull-up) for logic 1. This mode is required for bidirectional buses where multiple devices share the same line: Page 1 BITSTREAM Command User Manual - PS/2 keyboard/mouse interfaces - I2C-like protocols - Any bus requiring wired-AND logic Important considerations for open-collector mode: 1. Initial state: The pin is automatically initialized to high-impedance (HIGH) when the command is executed. Any prior pin state set by the user is overridden. 2. First transition is always LOW: Since the pin starts HIGH (hi-Z), the first toggle always drives the pin LOW. 3. Even number of transitions required: The count parameter must specify an even number of transitions. This ensures the pin returns to the HIGH (hi-Z) idle state after transmission. An error is generated if an odd count is specified. Note: When using open-collector mode, ensure appropriate pull-up resistors are connected to the signal lines (typically 4.7kOhm to 10kOhm to VCC). Dual Pin Operation When two pins are specified, both bitstreams run simultaneously with their timing events merged chronologically. This enables: 1. Two Independent Signals: Generate clock and data lines for protocols like PS/2 2. Carrier Modulation: Use the same pin for both channels to modulate a carrier frequency with an envelope (e.g., IR protocols) Same Pin for Both Channels When pin1 equals pin2, the two channels control the same physical pin. The logic parameter determines how the logical states combine: XOR Mode (logic = 0, default): - The pin toggles on every event from either channel - Original behavior for amplitude modulation where toggles interrupt the waveform AND Mode (logic = 1): - Each channel maintains a logical state (HIGH/LOW) - Physical output is HIGH only when BOTH channels are logically HIGH - Ideal for IR carrier modulation: carrier toggles fast, envelope enables/disables - The carrier only appears on the output when the envelope is "open" OR Mode (logic = 2): - Physical output is HIGH when EITHER channel is logically HIGH - Useful for combining two pulse trains Example use case for AND mode (IR modulation): - Channel 1: 38kHz carrier (rapid toggling between HIGH and LOW) - Channel 2: Envelope (slow transitions: HIGH=carrier enabled, LOW=carrier disabled) - Result: 38kHz bursts only during envelope HIGH periods Timing Accuracy Page 2 BITSTREAM Command User Manual - Timing values are specified in microseconds - Maximum timing value: 67,108 microseconds (~67ms) - Minimum recommended timing: ~1-2 microseconds (depends on CPU speed) - Interrupts are disabled during transmission for maximum accuracy - The first toggle occurs after the first timing value elapses How It Works 1. The pin starts in its current state (typically low if just configured as output) 2. For each timing value in sequence: - Wait for the specified duration - Toggle the pin state 3. In dual-pin mode, events from both arrays are processed in chronological order 4. If events on different pins occur at the same time, both are processed Examples Example 1: Simple Square Wave Generate a 1kHz square wave (500µs high, 500µs low): Dim timing(100) As Integer Local i As Integer ' Fill array with 500µs intervals For i = 0 To 99 timing(i) = 500 Next i SetPin GP15, DOUT Pin(GP15) = 0 BITSTREAM GP15, 100, timing() Example 2: NEC IR Protocol with AND Logic Generate a complete NEC IR remote control signal using AND logic for carrier gating: ' NEC IR Transmitter - Address 123, Command 107 ' Uses AND logic: output = carrier AND envelope ' Carrier toggles at 38kHz; envelope gates carrier on/off Const IR_PIN = 15 Const CARRIER_PERIOD = 13 ' microseconds (half period for 38kHz) Const PULSE_562 = 562 Const SPACE_562 = 562 Const SPACE_1687 = 1687 Const LEADER_PULSE = 9000 Const LEADER_SPACE = 4500 Const ADDRESS = 123 Const COMMAND = 107 Page 3 BITSTREAM Command User Manual Dim envelope(100) As Integer Dim envIdx As Integer = 0 ' Leader: 9ms pulse, 4.5ms space envelope(envIdx) = 0 : envIdx = envIdx + 1 ' t=0: enable carrier envelope(envIdx) = LEADER_PULSE : envIdx = envIdx + 1 ' t=9000: disable for space envelope(envIdx) = LEADER_SPACE : envIdx = envIdx + 1 ' t=13500: enable for bits Sub AddBit(bitVal As Integer) Local space As Integer If bitVal = 0 Then space = SPACE_562 Else space = SPACE_1687 envelope(envIdx) = PULSE_562 : envIdx = envIdx + 1 ' Disable after pulse envelope(envIdx) = space : envIdx = envIdx + 1 ' Enable after space End Sub ' Send address, inverted address, command, inverted command (LSB first) Dim i As Integer For i = 0 To 7 : AddBit((ADDRESS >> i) And 1) : Next i Dim invAddr As Integer = (Not ADDRESS) And &HFF For i = 0 To 7 : AddBit((invAddr >> i) And 1) : Next i For i = 0 To 7 : AddBit((COMMAND >> i) And 1) : Next i Dim invCmd As Integer = (Not COMMAND) And &HFF For i = 0 To 7 : AddBit((invCmd >> i) And 1) : Next i ' Final pulse envelope(envIdx) = PULSE_562 : envIdx = envIdx + 1 ' Calculate carrier transitions needed Dim totalTime As Integer = 0 For i = 0 To envIdx - 1 : totalTime = totalTime + envelope(i) : Next i Dim carrierCount As Integer = (totalTime \ CARRIER_PERIOD) + 50 Dim carrier(carrierCount) As Integer carrier(0) = 0 ' First toggle at t=0 For i = 1 To carrierCount - 1 : carrier(i) = CARRIER_PERIOD : Next i SetPin IR_PIN, DOUT Pin(IR_PIN) = 0 ' AND logic (1): carrier appears only when envelope is HIGH BITSTREAM IR_PIN, carrierCount, carrier(), 0, IR_PIN, envIdx, envelope(), 0, 1 Print "NEC IR sent!" Example 3: PS/2 Keyboard Scan Code Send a PS/2 keyboard scan code using open-collector mode: ' PS/2 Keyboard Scan Code Transmitter ' Uses dual bitstream with open-collector mode Const CLK_PIN = 15 Const DAT_PIN = 16 Const CLK_LOW = 40 ' Clock low time (µs) Const CLK_HIGH = 40 ' Clock high time (µs) Const INIT_DELAY = 50 ' Initial delay before first clock Page 4 BITSTREAM Command User Manual ' Transmit a PS/2 scan code Sub PS2_Send(scanCode As Integer) Local bits(10) As Integer Local clkTiming(30) As Integer Local datTiming(30) As Integer Local clkIdx As Integer = 0 Local datIdx As Integer = 0 Local currentData As Integer = 1 ' Data starts HIGH (hi-Z) Local dataTime As Integer = 0 Local bitVal As Integer Local i As Integer Local parity As Integer Local count As Integer = 0 ' Calculate parity (odd parity) For i = 0 To 7 If (scanCode >> i) And 1 Then count = count + 1 Next i parity = (count + 1) And 1 ' Build the 11-bit frame: Start, D0-D7, Parity, Stop bits(0) = 0 ' Start bit For i = 0 To 7 bits(i + 1) = (scanCode >> i) And 1 Next i bits(9) = parity bits(10) = 1 ' Stop bit ' First bit - data changes before first clock falling edge bitVal = bits(0) If bitVal <> currentData Then datTiming(datIdx) = INIT_DELAY - 5 : datIdx = datIdx + 1 currentData = bitVal dataTime = 5 Else dataTime = INIT_DELAY EndIf ' First clock transitions clkTiming(clkIdx) = INIT_DELAY : clkIdx = clkIdx + 1 clkTiming(clkIdx) = CLK_LOW : clkIdx = clkIdx + 1 ' Process remaining bits (1-10) For i = 1 To 10 bitVal = bits(i) If bitVal <> currentData Then datTiming(datIdx) = dataTime + CLK_LOW + 5 : datIdx = datIdx + 1 currentData = bitVal dataTime = CLK_HIGH - 5 Else dataTime = dataTime + CLK_LOW + CLK_HIGH EndIf Page 5 BITSTREAM Command User Manual clkTiming(clkIdx) = CLK_HIGH : clkIdx = clkIdx + 1 clkTiming(clkIdx) = CLK_LOW : clkIdx = clkIdx + 1 Next i ' Return data to HIGH if needed (ensure even transitions) If currentData = 0 Then datTiming(datIdx) = dataTime + CLK_LOW + CLK_HIGH : datIdx = datIdx + 1 EndIf If (datIdx And 1) = 1 Then datTiming(datIdx) = 50 : datIdx = datIdx + 1 EndIf ' Transmit using open-collector mode BITSTREAM CLK_PIN, clkIdx, clkTiming(), 1, DAT_PIN, datIdx, datTiming(), 1 End Sub ' Initialize and send scan code for 'A' SetPin CLK_PIN, DOUT SetPin DAT_PIN, DOUT PS2_Send(&H1C) Print "PS/2 scan code sent!" Notes - The pin must be configured as a digital output (DOUT) or unconfigured before use - Interrupts are disabled during transmission to ensure timing accuracy - For very long transmissions, be aware that other time-critical operations will be blocked - In push-pull mode, the pin starts in whatever state you set it to before calling BITSTREAM - In open-collector mode, the pin is forced to high-impedance (HIGH) at the start, and the count must be even to ensure it returns to HIGH - Array indices start at 0; ensure the array has at least count elements Error Messages Error Cause Invalid pin Pin number is out of range or refers to a reserved pin Pin already in use Pin is configured for another function Array too small Array has fewer elements than the specified count Number range Timing value exceeds 67,108 microseconds or is negative Open-collector mode requires even number of Count must be even when using open-collector mode (mode = 1) transitions Logic parameter only valid when both pins are the The logic parameter (9th) can only be used when pin1 = pin2 same Syntax error Incorrect number of parameters (must be 3, 4, 7, 8, or 9) Page 6 BITSTREAM Command User Manual See Also - SETPIN - Configure pin function - PIN() - Read or write digital pin state - PULSE - Generate a single pulse - PWM - Generate continuous PWM output Page 7