1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * Driver definitions for the FTDI USB Single Port Serial Converter - 4 * known as FTDI_SIO (Serial Input/Output application of the chipset) 5 * 6 * For USB vendor/product IDs (VID/PID), please see ftdi_sio_ids.h 7 * 8 * 9 * The example I have is known as the USC-1000 which is available from 10 * http://www.dse.co.nz - cat no XH4214 It looks similar to this: 11 * http://www.dansdata.com/usbser.htm but I can't be sure There are other 12 * USC-1000s which don't look like my device though so beware! 13 * 14 * The device is based on the FTDI FT8U100AX chip. It has a DB25 on one side, 15 * USB on the other. 16 * 17 * Thanx to FTDI (http://www.ftdichip.com) for so kindly providing details 18 * of the protocol required to talk to the device and ongoing assistence 19 * during development. 20 * 21 * Bill Ryder - bryder@sgi.com formerly of Silicon Graphics, Inc.- wrote the 22 * FTDI_SIO implementation. 23 * 24 */ 25 26 /* Commands */ 27 #define FTDI_SIO_RESET 0 /* Reset the port */ 28 #define FTDI_SIO_MODEM_CTRL 1 /* Set the modem control register */ 29 #define FTDI_SIO_SET_FLOW_CTRL 2 /* Set flow control register */ 30 #define FTDI_SIO_SET_BAUD_RATE 3 /* Set baud rate */ 31 #define FTDI_SIO_SET_DATA 4 /* Set the data characteristics of 32 the port */ 33 #define FTDI_SIO_GET_MODEM_STATUS 5 /* Retrieve current value of modem 34 status register */ 35 #define FTDI_SIO_SET_EVENT_CHAR 6 /* Set the event character */ 36 #define FTDI_SIO_SET_ERROR_CHAR 7 /* Set the error character */ 37 #define FTDI_SIO_SET_LATENCY_TIMER 9 /* Set the latency timer */ 38 #define FTDI_SIO_GET_LATENCY_TIMER 0x0a /* Get the latency timer */ 39 #define FTDI_SIO_SET_BITMODE 0x0b /* Set bitbang mode */ 40 #define FTDI_SIO_READ_PINS 0x0c /* Read immediate value of pins */ 41 #define FTDI_SIO_READ_EEPROM 0x90 /* Read EEPROM */ 42 43 /* Channel indices for FT2232, FT2232H and FT4232H devices */ 44 #define CHANNEL_A 1 45 #define CHANNEL_B 2 46 #define CHANNEL_C 3 47 #define CHANNEL_D 4 48 49 50 /* 51 * BmRequestType: 1100 0000b 52 * bRequest: FTDI_E2_READ 53 * wValue: 0 54 * wIndex: Address of word to read 55 * wLength: 2 56 * Data: Will return a word of data from E2Address 57 * 58 */ 59 60 /* Port Identifier Table */ 61 #define PIT_DEFAULT 0 /* SIOA */ 62 #define PIT_SIOA 1 /* SIOA */ 63 /* The device this driver is tested with one has only one port */ 64 #define PIT_SIOB 2 /* SIOB */ 65 #define PIT_PARALLEL 3 /* Parallel */ 66 67 /* FTDI_SIO_RESET */ 68 #define FTDI_SIO_RESET_REQUEST FTDI_SIO_RESET 69 #define FTDI_SIO_RESET_REQUEST_TYPE 0x40 70 #define FTDI_SIO_RESET_SIO 0 71 #define FTDI_SIO_RESET_PURGE_RX 1 72 #define FTDI_SIO_RESET_PURGE_TX 2 73 74 /* 75 * BmRequestType: 0100 0000B 76 * bRequest: FTDI_SIO_RESET 77 * wValue: Control Value 78 * 0 = Reset SIO 79 * 1 = Purge RX buffer 80 * 2 = Purge TX buffer 81 * wIndex: Port 82 * wLength: 0 83 * Data: None 84 * 85 * The Reset SIO command has this effect: 86 * 87 * Sets flow control set to 'none' 88 * Event char = $0D 89 * Event trigger = disabled 90 * Purge RX buffer 91 * Purge TX buffer 92 * Clear DTR 93 * Clear RTS 94 * baud and data format not reset 95 * 96 * The Purge RX and TX buffer commands affect nothing except the buffers 97 * 98 */ 99 100 /* FTDI_SIO_SET_BAUDRATE */ 101 #define FTDI_SIO_SET_BAUDRATE_REQUEST_TYPE 0x40 102 #define FTDI_SIO_SET_BAUDRATE_REQUEST 3 103 104 /* 105 * BmRequestType: 0100 0000B 106 * bRequest: FTDI_SIO_SET_BAUDRATE 107 * wValue: BaudDivisor value - see below 108 * wIndex: Port 109 * wLength: 0 110 * Data: None 111 * The BaudDivisor values are calculated as follows: 112 * - BaseClock is either 12000000 or 48000000 depending on the device. 113 * FIXME: I wish I knew how to detect old chips to select proper base clock! 114 * - BaudDivisor is a fixed point number encoded in a funny way. 115 * (--WRONG WAY OF THINKING--) 116 * BaudDivisor is a fixed point number encoded with following bit weighs: 117 * (-2)(-1)(13..0). It is a radical with a denominator of 4, so values 118 * end with 0.0 (00...), 0.25 (10...), 0.5 (01...), and 0.75 (11...). 119 * (--THE REALITY--) 120 * The both-bits-set has quite different meaning from 0.75 - the chip 121 * designers have decided it to mean 0.125 instead of 0.75. 122 * This info looked up in FTDI application note "FT8U232 DEVICES \ Data Rates 123 * and Flow Control Consideration for USB to RS232". 124 * - BaudDivisor = (BaseClock / 16) / BaudRate, where the (=) operation should 125 * automagically re-encode the resulting value to take fractions into 126 * consideration. 127 * As all values are integers, some bit twiddling is in order: 128 * BaudDivisor = (BaseClock / 16 / BaudRate) | 129 * (((BaseClock / 2 / BaudRate) & 4) ? 0x4000 // 0.5 130 * : ((BaseClock / 2 / BaudRate) & 2) ? 0x8000 // 0.25 131 * : ((BaseClock / 2 / BaudRate) & 1) ? 0xc000 // 0.125 132 * : 0) 133 * 134 * For the FT232BM, a 17th divisor bit was introduced to encode the multiples 135 * of 0.125 missing from the FT8U232AM. Bits 16 to 14 are coded as follows 136 * (the first four codes are the same as for the FT8U232AM, where bit 16 is 137 * always 0): 138 * 000 - add .000 to divisor 139 * 001 - add .500 to divisor 140 * 010 - add .250 to divisor 141 * 011 - add .125 to divisor 142 * 100 - add .375 to divisor 143 * 101 - add .625 to divisor 144 * 110 - add .750 to divisor 145 * 111 - add .875 to divisor 146 * Bits 15 to 0 of the 17-bit divisor are placed in the urb value. Bit 16 is 147 * placed in bit 0 of the urb index. 148 * 149 * Note that there are a couple of special cases to support the highest baud 150 * rates. If the calculated divisor value is 1, this needs to be replaced with 151 * 0. Additionally for the FT232BM, if the calculated divisor value is 0x4001 152 * (1.5), this needs to be replaced with 0x0001 (1) (but this divisor value is 153 * not supported by the FT8U232AM). 154 */ 155 156 enum ftdi_sio_baudrate { 157 ftdi_sio_b300 = 0, 158 ftdi_sio_b600 = 1, 159 ftdi_sio_b1200 = 2, 160 ftdi_sio_b2400 = 3, 161 ftdi_sio_b4800 = 4, 162 ftdi_sio_b9600 = 5, 163 ftdi_sio_b19200 = 6, 164 ftdi_sio_b38400 = 7, 165 ftdi_sio_b57600 = 8, 166 ftdi_sio_b115200 = 9 167 }; 168 169 /* 170 * The ftdi_8U232AM_xxMHz_byyy constants have been removed. The encoded divisor 171 * values are calculated internally. 172 */ 173 #define FTDI_SIO_SET_DATA_REQUEST FTDI_SIO_SET_DATA 174 #define FTDI_SIO_SET_DATA_REQUEST_TYPE 0x40 175 #define FTDI_SIO_SET_DATA_PARITY_NONE (0x0 << 8) 176 #define FTDI_SIO_SET_DATA_PARITY_ODD (0x1 << 8) 177 #define FTDI_SIO_SET_DATA_PARITY_EVEN (0x2 << 8) 178 #define FTDI_SIO_SET_DATA_PARITY_MARK (0x3 << 8) 179 #define FTDI_SIO_SET_DATA_PARITY_SPACE (0x4 << 8) 180 #define FTDI_SIO_SET_DATA_STOP_BITS_1 (0x0 << 11) 181 #define FTDI_SIO_SET_DATA_STOP_BITS_15 (0x1 << 11) 182 #define FTDI_SIO_SET_DATA_STOP_BITS_2 (0x2 << 11) 183 #define FTDI_SIO_SET_BREAK (0x1 << 14) 184 /* FTDI_SIO_SET_DATA */ 185 186 /* 187 * BmRequestType: 0100 0000B 188 * bRequest: FTDI_SIO_SET_DATA 189 * wValue: Data characteristics (see below) 190 * wIndex: Port 191 * wLength: 0 192 * Data: No 193 * 194 * Data characteristics 195 * 196 * B0..7 Number of data bits 197 * B8..10 Parity 198 * 0 = None 199 * 1 = Odd 200 * 2 = Even 201 * 3 = Mark 202 * 4 = Space 203 * B11..13 Stop Bits 204 * 0 = 1 205 * 1 = 1.5 206 * 2 = 2 207 * B14 208 * 1 = TX ON (break) 209 * 0 = TX OFF (normal state) 210 * B15 Reserved 211 * 212 */ 213 214 215 216 /* FTDI_SIO_MODEM_CTRL */ 217 #define FTDI_SIO_SET_MODEM_CTRL_REQUEST_TYPE 0x40 218 #define FTDI_SIO_SET_MODEM_CTRL_REQUEST FTDI_SIO_MODEM_CTRL 219 220 /* 221 * BmRequestType: 0100 0000B 222 * bRequest: FTDI_SIO_MODEM_CTRL 223 * wValue: ControlValue (see below) 224 * wIndex: Port 225 * wLength: 0 226 * Data: None 227 * 228 * NOTE: If the device is in RTS/CTS flow control, the RTS set by this 229 * command will be IGNORED without an error being returned 230 * Also - you can not set DTR and RTS with one control message 231 */ 232 233 #define FTDI_SIO_SET_DTR_MASK 0x1 234 #define FTDI_SIO_SET_DTR_HIGH ((FTDI_SIO_SET_DTR_MASK << 8) | 1) 235 #define FTDI_SIO_SET_DTR_LOW ((FTDI_SIO_SET_DTR_MASK << 8) | 0) 236 #define FTDI_SIO_SET_RTS_MASK 0x2 237 #define FTDI_SIO_SET_RTS_HIGH ((FTDI_SIO_SET_RTS_MASK << 8) | 2) 238 #define FTDI_SIO_SET_RTS_LOW ((FTDI_SIO_SET_RTS_MASK << 8) | 0) 239 240 /* 241 * ControlValue 242 * B0 DTR state 243 * 0 = reset 244 * 1 = set 245 * B1 RTS state 246 * 0 = reset 247 * 1 = set 248 * B2..7 Reserved 249 * B8 DTR state enable 250 * 0 = ignore 251 * 1 = use DTR state 252 * B9 RTS state enable 253 * 0 = ignore 254 * 1 = use RTS state 255 * B10..15 Reserved 256 */ 257 258 /* FTDI_SIO_SET_FLOW_CTRL */ 259 #define FTDI_SIO_SET_FLOW_CTRL_REQUEST_TYPE 0x40 260 #define FTDI_SIO_SET_FLOW_CTRL_REQUEST FTDI_SIO_SET_FLOW_CTRL 261 #define FTDI_SIO_DISABLE_FLOW_CTRL 0x0 262 #define FTDI_SIO_RTS_CTS_HS (0x1 << 8) 263 #define FTDI_SIO_DTR_DSR_HS (0x2 << 8) 264 #define FTDI_SIO_XON_XOFF_HS (0x4 << 8) 265 /* 266 * BmRequestType: 0100 0000b 267 * bRequest: FTDI_SIO_SET_FLOW_CTRL 268 * wValue: Xoff/Xon 269 * wIndex: Protocol/Port - hIndex is protocol / lIndex is port 270 * wLength: 0 271 * Data: None 272 * 273 * hIndex protocol is: 274 * B0 Output handshaking using RTS/CTS 275 * 0 = disabled 276 * 1 = enabled 277 * B1 Output handshaking using DTR/DSR 278 * 0 = disabled 279 * 1 = enabled 280 * B2 Xon/Xoff handshaking 281 * 0 = disabled 282 * 1 = enabled 283 * 284 * A value of zero in the hIndex field disables handshaking 285 * 286 * If Xon/Xoff handshaking is specified, the hValue field should contain the 287 * XOFF character and the lValue field contains the XON character. 288 */ 289 290 /* 291 * FTDI_SIO_GET_LATENCY_TIMER 292 * 293 * Set the timeout interval. The FTDI collects data from the 294 * device, transmitting it to the host when either A) 62 bytes are 295 * received, or B) the timeout interval has elapsed and the buffer 296 * contains at least 1 byte. Setting this value to a small number 297 * can dramatically improve performance for applications which send 298 * small packets, since the default value is 16ms. 299 */ 300 #define FTDI_SIO_GET_LATENCY_TIMER_REQUEST FTDI_SIO_GET_LATENCY_TIMER 301 #define FTDI_SIO_GET_LATENCY_TIMER_REQUEST_TYPE 0xC0 302 303 /* 304 * BmRequestType: 1100 0000b 305 * bRequest: FTDI_SIO_GET_LATENCY_TIMER 306 * wValue: 0 307 * wIndex: Port 308 * wLength: 0 309 * Data: latency (on return) 310 */ 311 312 /* 313 * FTDI_SIO_SET_LATENCY_TIMER 314 * 315 * Set the timeout interval. The FTDI collects data from the 316 * device, transmitting it to the host when either A) 62 bytes are 317 * received, or B) the timeout interval has elapsed and the buffer 318 * contains at least 1 byte. Setting this value to a small number 319 * can dramatically improve performance for applications which send 320 * small packets, since the default value is 16ms. 321 */ 322 #define FTDI_SIO_SET_LATENCY_TIMER_REQUEST FTDI_SIO_SET_LATENCY_TIMER 323 #define FTDI_SIO_SET_LATENCY_TIMER_REQUEST_TYPE 0x40 324 325 /* 326 * BmRequestType: 0100 0000b 327 * bRequest: FTDI_SIO_SET_LATENCY_TIMER 328 * wValue: Latency (milliseconds) 329 * wIndex: Port 330 * wLength: 0 331 * Data: None 332 * 333 * wValue: 334 * B0..7 Latency timer 335 * B8..15 0 336 * 337 */ 338 339 /* 340 * FTDI_SIO_SET_EVENT_CHAR 341 * 342 * Set the special event character for the specified communications port. 343 * If the device sees this character it will immediately return the 344 * data read so far - rather than wait 40ms or until 62 bytes are read 345 * which is what normally happens. 346 */ 347 348 349 #define FTDI_SIO_SET_EVENT_CHAR_REQUEST FTDI_SIO_SET_EVENT_CHAR 350 #define FTDI_SIO_SET_EVENT_CHAR_REQUEST_TYPE 0x40 351 352 353 /* 354 * BmRequestType: 0100 0000b 355 * bRequest: FTDI_SIO_SET_EVENT_CHAR 356 * wValue: EventChar 357 * wIndex: Port 358 * wLength: 0 359 * Data: None 360 * 361 * wValue: 362 * B0..7 Event Character 363 * B8 Event Character Processing 364 * 0 = disabled 365 * 1 = enabled 366 * B9..15 Reserved 367 * 368 */ 369 370 /* FTDI_SIO_SET_ERROR_CHAR */ 371 372 /* 373 * Set the parity error replacement character for the specified communications 374 * port 375 */ 376 377 /* 378 * BmRequestType: 0100 0000b 379 * bRequest: FTDI_SIO_SET_EVENT_CHAR 380 * wValue: Error Char 381 * wIndex: Port 382 * wLength: 0 383 * Data: None 384 * 385 *Error Char 386 * B0..7 Error Character 387 * B8 Error Character Processing 388 * 0 = disabled 389 * 1 = enabled 390 * B9..15 Reserved 391 * 392 */ 393 394 /* FTDI_SIO_GET_MODEM_STATUS */ 395 /* Retrieve the current value of the modem status register */ 396 397 #define FTDI_SIO_GET_MODEM_STATUS_REQUEST_TYPE 0xc0 398 #define FTDI_SIO_GET_MODEM_STATUS_REQUEST FTDI_SIO_GET_MODEM_STATUS 399 #define FTDI_SIO_CTS_MASK 0x10 400 #define FTDI_SIO_DSR_MASK 0x20 401 #define FTDI_SIO_RI_MASK 0x40 402 #define FTDI_SIO_RLSD_MASK 0x80 403 /* 404 * BmRequestType: 1100 0000b 405 * bRequest: FTDI_SIO_GET_MODEM_STATUS 406 * wValue: zero 407 * wIndex: Port 408 * wLength: 1 409 * Data: Status 410 * 411 * One byte of data is returned 412 * B0..3 0 413 * B4 CTS 414 * 0 = inactive 415 * 1 = active 416 * B5 DSR 417 * 0 = inactive 418 * 1 = active 419 * B6 Ring Indicator (RI) 420 * 0 = inactive 421 * 1 = active 422 * B7 Receive Line Signal Detect (RLSD) 423 * 0 = inactive 424 * 1 = active 425 */ 426 427 /* FTDI_SIO_SET_BITMODE */ 428 #define FTDI_SIO_SET_BITMODE_REQUEST_TYPE 0x40 429 #define FTDI_SIO_SET_BITMODE_REQUEST FTDI_SIO_SET_BITMODE 430 431 /* Possible bitmodes for FTDI_SIO_SET_BITMODE_REQUEST */ 432 #define FTDI_SIO_BITMODE_RESET 0x00 433 #define FTDI_SIO_BITMODE_CBUS 0x20 434 435 /* FTDI_SIO_READ_PINS */ 436 #define FTDI_SIO_READ_PINS_REQUEST_TYPE 0xc0 437 #define FTDI_SIO_READ_PINS_REQUEST FTDI_SIO_READ_PINS 438 439 /* 440 * FTDI_SIO_READ_EEPROM 441 * 442 * EEPROM format found in FTDI AN_201, "FT-X MTP memory Configuration", 443 * http://www.ftdichip.com/Support/Documents/AppNotes/AN_201_FT-X%20MTP%20Memory%20Configuration.pdf 444 */ 445 #define FTDI_SIO_READ_EEPROM_REQUEST_TYPE 0xc0 446 #define FTDI_SIO_READ_EEPROM_REQUEST FTDI_SIO_READ_EEPROM 447 448 #define FTDI_FTX_CBUS_MUX_GPIO 0x8 449 #define FTDI_FT232R_CBUS_MUX_GPIO 0xa 450 451 452 /* Descriptors returned by the device 453 * 454 * Device Descriptor 455 * 456 * Offset Field Size Value Description 457 * 0 bLength 1 0x12 Size of descriptor in bytes 458 * 1 bDescriptorType 1 0x01 DEVICE Descriptor Type 459 * 2 bcdUSB 2 0x0110 USB Spec Release Number 460 * 4 bDeviceClass 1 0x00 Class Code 461 * 5 bDeviceSubClass 1 0x00 SubClass Code 462 * 6 bDeviceProtocol 1 0x00 Protocol Code 463 * 7 bMaxPacketSize0 1 0x08 Maximum packet size for endpoint 0 464 * 8 idVendor 2 0x0403 Vendor ID 465 * 10 idProduct 2 0x8372 Product ID (FTDI_SIO_PID) 466 * 12 bcdDevice 2 0x0001 Device release number 467 * 14 iManufacturer 1 0x01 Index of man. string desc 468 * 15 iProduct 1 0x02 Index of prod string desc 469 * 16 iSerialNumber 1 0x02 Index of serial nmr string desc 470 * 17 bNumConfigurations 1 0x01 Number of possible configurations 471 * 472 * Configuration Descriptor 473 * 474 * Offset Field Size Value 475 * 0 bLength 1 0x09 Size of descriptor in bytes 476 * 1 bDescriptorType 1 0x02 CONFIGURATION Descriptor Type 477 * 2 wTotalLength 2 0x0020 Total length of data 478 * 4 bNumInterfaces 1 0x01 Number of interfaces supported 479 * 5 bConfigurationValue 1 0x01 Argument for SetCOnfiguration() req 480 * 6 iConfiguration 1 0x02 Index of config string descriptor 481 * 7 bmAttributes 1 0x20 Config characteristics Remote Wakeup 482 * 8 MaxPower 1 0x1E Max power consumption 483 * 484 * Interface Descriptor 485 * 486 * Offset Field Size Value 487 * 0 bLength 1 0x09 Size of descriptor in bytes 488 * 1 bDescriptorType 1 0x04 INTERFACE Descriptor Type 489 * 2 bInterfaceNumber 1 0x00 Number of interface 490 * 3 bAlternateSetting 1 0x00 Value used to select alternate 491 * 4 bNumEndpoints 1 0x02 Number of endpoints 492 * 5 bInterfaceClass 1 0xFF Class Code 493 * 6 bInterfaceSubClass 1 0xFF Subclass Code 494 * 7 bInterfaceProtocol 1 0xFF Protocol Code 495 * 8 iInterface 1 0x02 Index of interface string description 496 * 497 * IN Endpoint Descriptor 498 * 499 * Offset Field Size Value 500 * 0 bLength 1 0x07 Size of descriptor in bytes 501 * 1 bDescriptorType 1 0x05 ENDPOINT descriptor type 502 * 2 bEndpointAddress 1 0x82 Address of endpoint 503 * 3 bmAttributes 1 0x02 Endpoint attributes - Bulk 504 * 4 bNumEndpoints 2 0x0040 maximum packet size 505 * 5 bInterval 1 0x00 Interval for polling endpoint 506 * 507 * OUT Endpoint Descriptor 508 * 509 * Offset Field Size Value 510 * 0 bLength 1 0x07 Size of descriptor in bytes 511 * 1 bDescriptorType 1 0x05 ENDPOINT descriptor type 512 * 2 bEndpointAddress 1 0x02 Address of endpoint 513 * 3 bmAttributes 1 0x02 Endpoint attributes - Bulk 514 * 4 bNumEndpoints 2 0x0040 maximum packet size 515 * 5 bInterval 1 0x00 Interval for polling endpoint 516 * 517 * DATA FORMAT 518 * 519 * IN Endpoint 520 * 521 * The device reserves the first two bytes of data on this endpoint to contain 522 * the current values of the modem and line status registers. In the absence of 523 * data, the device generates a message consisting of these two status bytes 524 * every 40 ms 525 * 526 * Byte 0: Modem Status 527 * 528 * Offset Description 529 * B0 Reserved - must be 1 530 * B1 Reserved - must be 0 531 * B2 Reserved - must be 0 532 * B3 Reserved - must be 0 533 * B4 Clear to Send (CTS) 534 * B5 Data Set Ready (DSR) 535 * B6 Ring Indicator (RI) 536 * B7 Receive Line Signal Detect (RLSD) 537 * 538 * Byte 1: Line Status 539 * 540 * Offset Description 541 * B0 Data Ready (DR) 542 * B1 Overrun Error (OE) 543 * B2 Parity Error (PE) 544 * B3 Framing Error (FE) 545 * B4 Break Interrupt (BI) 546 * B5 Transmitter Holding Register (THRE) 547 * B6 Transmitter Empty (TEMT) 548 * B7 Error in RCVR FIFO 549 * 550 */ 551 #define FTDI_RS0_CTS (1 << 4) 552 #define FTDI_RS0_DSR (1 << 5) 553 #define FTDI_RS0_RI (1 << 6) 554 #define FTDI_RS0_RLSD (1 << 7) 555 556 #define FTDI_RS_DR 1 557 #define FTDI_RS_OE (1<<1) 558 #define FTDI_RS_PE (1<<2) 559 #define FTDI_RS_FE (1<<3) 560 #define FTDI_RS_BI (1<<4) 561 #define FTDI_RS_THRE (1<<5) 562 #define FTDI_RS_TEMT (1<<6) 563 #define FTDI_RS_FIFO (1<<7) 564 565 /* 566 * OUT Endpoint 567 * 568 * This device reserves the first bytes of data on this endpoint contain the 569 * length and port identifier of the message. For the FTDI USB Serial converter 570 * the port identifier is always 1. 571 * 572 * Byte 0: Line Status 573 * 574 * Offset Description 575 * B0 Reserved - must be 1 576 * B1 Reserved - must be 0 577 * B2..7 Length of message - (not including Byte 0) 578 * 579 */ 580