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6658905f 1//-----------------------------------------------------------------------------
2// ISO14443-A support for the Proxmark III
3// Gerhard de Koning Gans, April 2008
4//-----------------------------------------------------------------------------
5
7bc95e2e 6// constants for the different modes:
7`define SNIFFER 3'b000
8`define TAGSIM_LISTEN 3'b001
9`define TAGSIM_MOD 3'b010
10`define READER_LISTEN 3'b011
11`define READER_MOD 3'b100
12
6658905f 13module hi_iso14443a(
14 pck0, ck_1356meg, ck_1356megb,
15 pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,
16 adc_d, adc_clk,
17 ssp_frame, ssp_din, ssp_dout, ssp_clk,
18 cross_hi, cross_lo,
19 dbg,
20 mod_type
21);
22 input pck0, ck_1356meg, ck_1356megb;
23 output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
24 input [7:0] adc_d;
25 output adc_clk;
26 input ssp_dout;
27 output ssp_frame, ssp_din, ssp_clk;
28 input cross_hi, cross_lo;
29 output dbg;
30 input [2:0] mod_type;
31
6658905f 32
d714d3ef 33wire adc_clk = ck_1356meg;
34
6658905f 35
d714d3ef 36
37////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
38// Reader -> PM3:
39// detecting and shaping the reader's signal. Reader will modulate the carrier by 100% (signal is either on or off). Use a
40// hysteresis (Schmitt Trigger) to avoid false triggers during slowly increasing or decreasing carrier amplitudes
41reg after_hysteresis;
6658905f 42reg [11:0] has_been_low_for;
7bc95e2e 43
6658905f 44always @(negedge adc_clk)
45begin
d714d3ef 46 if(adc_d >= 16) after_hysteresis <= 1'b1; // U >= 1,14V -> after_hysteresis = 1
47 else if(adc_d < 8) after_hysteresis <= 1'b0; // U < 1,04V -> after_hysteresis = 0
48 // Note: was >= 3,53V and <= 1,19V. The new trigger values allow more reliable detection of the first bit
49 // (it might not reach 3,53V due to the high time constant of the high pass filter in the analogue RF part).
50 // In addition, the new values are more in line with ISO14443-2: "The PICC shall detect the ”End of Pause” after the field exceeds
51 // 5% of H_INITIAL and before it exceeds 60% of H_INITIAL." Depending on the signal strength, 60% might well be less than 3,53V.
6658905f 52
6658905f 53
d714d3ef 54 // detecting a loss of reader's field (adc_d < 192 for 4096 clock cycles). If this is the case,
55 // set the detected reader signal (after_hysteresis) to '1' (unmodulated)
56 if(adc_d >= 192)
6658905f 57 begin
7bc95e2e 58 has_been_low_for <= 12'd0;
6658905f 59 end
60 else
61 begin
62 if(has_been_low_for == 12'd4095)
63 begin
64 has_been_low_for <= 12'd0;
d714d3ef 65 after_hysteresis <= 1'b1;
6658905f 66 end
67 else
7bc95e2e 68 begin
6658905f 69 has_been_low_for <= has_been_low_for + 1;
7bc95e2e 70 end
6658905f 71 end
d714d3ef 72
6658905f 73end
74
7bc95e2e 75
76
d714d3ef 77////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
78// Reader -> PM3
79// detect when a reader is active (modulating). We assume that the reader is active, if we see the carrier off for at least 8
80// carrier cycles. We assume that the reader is inactive, if the carrier stayed high for at least 256 carrier cycles.
81reg deep_modulation;
82reg [2:0] deep_counter;
83reg [8:0] saw_deep_modulation;
e691fc45 84
d714d3ef 85always @(negedge adc_clk)
86begin
87 if(~(| adc_d[7:0])) // if adc_d == 0 (U <= 0,94V)
88 begin
89 if(deep_counter == 3'd7) // adc_d == 0 for 8 adc_clk ticks -> deep_modulation (by reader)
90 begin
91 deep_modulation <= 1'b1;
92 saw_deep_modulation <= 8'd0;
93 end
94 else
95 deep_counter <= deep_counter + 1;
96 end
97 else
98 begin
99 deep_counter <= 3'd0;
100 if(saw_deep_modulation == 8'd255) // adc_d != 0 for 256 adc_clk ticks -> deep_modulation is over, probably waiting for tag's response
101 deep_modulation <= 1'b0;
102 else
103 saw_deep_modulation <= saw_deep_modulation + 1;
104 end
105end
e691fc45 106
6658905f 107
6658905f 108
d714d3ef 109////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
110// Tag -> PM3
111// filter the input for a tag's signal. The filter box needs the 4 previous input values and is a gaussian derivative filter
112// for noise reduction and edge detection.
113// store 4 previous samples:
114reg [7:0] input_prev_4, input_prev_3, input_prev_2, input_prev_1;
30364d27 115
6658905f 116always @(negedge adc_clk)
117begin
d714d3ef 118 input_prev_4 <= input_prev_3;
119 input_prev_3 <= input_prev_2;
120 input_prev_2 <= input_prev_1;
121 input_prev_1 <= adc_d;
122end
123
30364d27 124// adc_d_filtered = 2*input_prev4 + 1*input_prev3 + 0*input_prev2 - 1*input_prev1 - 2*input
125// = (2*input_prev4 + input_prev3) - (2*input + input_prev1)
126wire [8:0] input_prev_4_times_2 = input_prev_4 << 1;
127wire [8:0] adc_d_times_2 = adc_d << 1;
128
129wire [9:0] tmp1 = input_prev_4_times_2 + input_prev_3;
130wire [9:0] tmp2 = adc_d_times_2 + input_prev_1;
131
132// convert intermediate signals to signed and calculate the filter output
133wire signed [10:0] adc_d_filtered = {1'b0, tmp1} - {1'b0, tmp2};
134
d714d3ef 135
6658905f 136
d714d3ef 137////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
138// internal FPGA timing. Maximum required period is 128 carrier clock cycles for a full 8 Bit transfer to ARM. (i.e. we need a
139// 7 bit counter). Adjust its frequency to external reader's clock when simulating a tag or sniffing.
140reg pre_after_hysteresis;
141reg [3:0] reader_falling_edge_time;
142reg [6:0] negedge_cnt;
143
144always @(negedge adc_clk)
145begin
146 // detect a reader signal's falling edge and remember its timing:
147 pre_after_hysteresis <= after_hysteresis;
148 if (pre_after_hysteresis && ~after_hysteresis)
149 begin
150 reader_falling_edge_time[3:0] <= negedge_cnt[3:0];
151 end
152
153 // adjust internal timer counter if necessary:
154 if (negedge_cnt[3:0] == 4'd13 && (mod_type == `SNIFFER || mod_type == `TAGSIM_LISTEN) && deep_modulation)
6658905f 155 begin
d714d3ef 156 if (reader_falling_edge_time == 4'd1) // reader signal changes right after sampling. Better sample earlier next time.
6658905f 157 begin
d714d3ef 158 negedge_cnt <= negedge_cnt + 2; // time warp
159 end
160 else if (reader_falling_edge_time == 4'd0) // reader signal changes right before sampling. Better sample later next time.
161 begin
162 negedge_cnt <= negedge_cnt; // freeze time
6658905f 163 end
164 else
165 begin
d714d3ef 166 negedge_cnt <= negedge_cnt + 1; // Continue as usual
6658905f 167 end
d714d3ef 168 reader_falling_edge_time[3:0] <= 4'd8; // adjust only once per detected edge
6658905f 169 end
d714d3ef 170 else if (negedge_cnt == 7'd127) // normal operation: count from 0 to 127
6658905f 171 begin
d714d3ef 172 negedge_cnt <= 0;
7bc95e2e 173 end
d714d3ef 174 else
175 begin
176 negedge_cnt <= negedge_cnt + 1;
177 end
178end
7bc95e2e 179
d714d3ef 180
181////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
182// Tag -> PM3:
183// determine best possible time for starting/resetting the modulation detector.
184reg [3:0] mod_detect_reset_time;
185
186always @(negedge adc_clk)
187begin
188 if (mod_type == `READER_LISTEN)
30364d27 189 // (our) reader signal changes at negedge_cnt[3:0]=9, tag response expected to start n*16+4 ticks later, further delayed by
190 // 3 ticks ADC conversion. The maximum filter output (edge detected) will be detected after subcarrier zero crossing (+7 ticks).
191 // To allow some timing variances, we want to have the maximum filter outputs well within the detection window, i.e.
192 // at mod_detect_reset_time+4 and mod_detect_reset_time+12 (-4 ticks).
193 // 9 + 4 + 3 + 7 - 4 = 19. 19 mod 16 = 3
7bc95e2e 194 begin
30364d27 195 mod_detect_reset_time <= 4'd4;
d714d3ef 196 end
197 else
198 if (mod_type == `SNIFFER)
199 begin
200 // detect a rising edge of reader's signal and sync modulation detector to the tag's answer:
201 if (~pre_after_hysteresis && after_hysteresis && deep_modulation)
202 // reader signal rising edge detected at negedge_cnt[3:0]. This signal had been delayed
203 // 9 ticks by the RF part + 3 ticks by the A/D converter + 1 tick to assign to after_hysteresis.
30364d27 204 // Then the same as above.
205 // - 9 - 3 - 1 + 4 + 3 + 7 - 4 = -3
e691fc45 206 begin
30364d27 207 mod_detect_reset_time <= negedge_cnt[3:0] - 4'd3;
e691fc45 208 end
7bc95e2e 209 end
d714d3ef 210end
211
212
213////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
214// Tag -> PM3:
215// modulation detector. Looks for the steepest falling and rising edges within a 16 clock period. If there is both a significant
216// falling and rising edge (in any order), a modulation is detected.
217reg signed [10:0] rx_mod_falling_edge_max;
218reg signed [10:0] rx_mod_rising_edge_max;
219reg curbit;
220
30364d27 221`define EDGE_DETECT_THRESHOLD 5
222
d714d3ef 223always @(negedge adc_clk)
224begin
225 if(negedge_cnt[3:0] == mod_detect_reset_time)
226 begin
227 // detect modulation signal: if modulating, there must have been a falling AND a rising edge
30364d27 228 if ((rx_mod_falling_edge_max > `EDGE_DETECT_THRESHOLD) && (rx_mod_rising_edge_max < -`EDGE_DETECT_THRESHOLD))
d714d3ef 229 curbit <= 1'b1; // modulation
230 else
231 curbit <= 1'b0; // no modulation
232 // reset modulation detector
233 rx_mod_rising_edge_max <= 0;
234 rx_mod_falling_edge_max <= 0;
235 end
236 else // look for steepest edges (slopes)
7bc95e2e 237 begin
238 if (adc_d_filtered > 0)
239 begin
240 if (adc_d_filtered > rx_mod_falling_edge_max)
241 rx_mod_falling_edge_max <= adc_d_filtered;
242 end
243 else
244 begin
30364d27 245 if (adc_d_filtered < rx_mod_rising_edge_max)
246 rx_mod_rising_edge_max <= adc_d_filtered;
7bc95e2e 247 end
248 end
249
d714d3ef 250end
251
e691fc45 252
e691fc45 253
d714d3ef 254////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
255// Tag+Reader -> PM3
256// sample 4 bits reader data and 4 bits tag data for sniffing
257reg [3:0] reader_data;
258reg [3:0] tag_data;
259
260always @(negedge adc_clk)
261begin
262 if(negedge_cnt[3:0] == 4'd0)
6658905f 263 begin
d714d3ef 264 reader_data[3:0] <= {reader_data[2:0], after_hysteresis};
265 tag_data[3:0] <= {tag_data[2:0], curbit};
266 end
267end
268
7bc95e2e 269
270
d714d3ef 271////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
30364d27 272// PM3 -> Reader:
d714d3ef 273// a delay line to ensure that we send the (emulated) tag's answer at the correct time according to ISO14443-3
274reg [31:0] mod_sig_buf;
275reg [4:0] mod_sig_ptr;
276reg mod_sig;
277
278always @(negedge adc_clk)
279begin
280 if(negedge_cnt[3:0] == 4'd0) // sample data at rising edge of ssp_clk - ssp_dout changes at the falling edge.
7bc95e2e 281 begin
d714d3ef 282 mod_sig_buf[31:2] <= mod_sig_buf[30:1]; // shift
283 if (~ssp_dout && ~mod_sig_buf[1])
284 mod_sig_buf[1] <= 1'b0; // delete the correction bit (a single 1 preceded and succeeded by 0)
7bc95e2e 285 else
d714d3ef 286 mod_sig_buf[1] <= mod_sig_buf[0];
287 mod_sig_buf[0] <= ssp_dout; // add new data to the delay line
288
289 mod_sig = mod_sig_buf[mod_sig_ptr]; // the delayed signal.
7bc95e2e 290 end
d714d3ef 291end
7bc95e2e 292
d7aa3739 293
294
d714d3ef 295////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
30364d27 296// PM3 -> Reader, internal timing:
d714d3ef 297// a timer for the 1172 cycles fdt (Frame Delay Time). Start the timer with a rising edge of the reader's signal.
298// set fdt_elapsed when we no longer need to delay data. Set fdt_indicator when we can start sending data.
299// Note: the FPGA only takes care for the 1172 delay. To achieve an additional 1236-1172=64 ticks delay, the ARM must send
300// a correction bit (before the start bit). The correction bit will be coded as 00010000, i.e. it adds 4 bits to the
301// transmission stream, causing the required additional delay.
302reg [10:0] fdt_counter;
303reg fdt_indicator, fdt_elapsed;
304reg [3:0] mod_sig_flip;
305reg [3:0] sub_carrier_cnt;
d7aa3739 306
d714d3ef 307// we want to achieve a delay of 1172. The RF part already has delayed the reader signals's rising edge
308// by 9 ticks, the ADC took 3 ticks and there is always a delay of 32 ticks by the mod_sig_buf. Therefore need to
309// count to 1172 - 9 - 3 - 32 = 1128
310`define FDT_COUNT 11'd1128
d7aa3739 311
d714d3ef 312// The ARM must not send too early, otherwise the mod_sig_buf will overflow, therefore signal that we are ready
313// with fdt_indicator. The mod_sig_buf can buffer 29 excess data bits, i.e. a maximum delay of 29 * 16 = 464 adc_clk ticks.
314// fdt_indicator could appear at ssp_din after 1 tick, the transfer needs 16 ticks, the ARM can send 128 ticks later.
315// 1128 - 464 - 1 - 128 - 8 = 535
316`define FDT_INDICATOR_COUNT 11'd535
d7aa3739 317
d714d3ef 318// reset on a pause in listen mode. I.e. the counter starts when the pause is over:
319assign fdt_reset = ~after_hysteresis && mod_type == `TAGSIM_LISTEN;
320
321always @(negedge adc_clk)
322begin
323 if (fdt_reset)
d7aa3739 324 begin
d714d3ef 325 fdt_counter <= 11'd0;
326 fdt_elapsed <= 1'b0;
327 fdt_indicator <= 1'b0;
328 end
329 else
330 begin
331 if(fdt_counter == `FDT_COUNT)
332 begin
333 if(~fdt_elapsed) // just reached fdt.
334 begin
335 mod_sig_flip <= negedge_cnt[3:0]; // start modulation at this time
336 sub_carrier_cnt <= 4'd0; // subcarrier phase in sync with start of modulation
337 fdt_elapsed <= 1'b1;
338 end
339 else
340 begin
341 sub_carrier_cnt <= sub_carrier_cnt + 1;
342 end
d7aa3739 343 end
d7aa3739 344 else
345 begin
d714d3ef 346 fdt_counter <= fdt_counter + 1;
d7aa3739 347 end
d7aa3739 348 end
349
d714d3ef 350 if(fdt_counter == `FDT_INDICATOR_COUNT) fdt_indicator <= 1'b1;
351end
352
d7aa3739 353
d714d3ef 354////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
355// PM3 -> Reader or Tag
356// assign a modulation signal to the antenna. This signal is either a delayed signal (to achieve fdt when sending to a reader)
357// or undelayed when sending to a tag
358reg mod_sig_coil;
d7aa3739 359
d714d3ef 360always @(negedge adc_clk)
361begin
362 if (mod_type == `TAGSIM_MOD) // need to take care of proper fdt timing
7bc95e2e 363 begin
d714d3ef 364 if(fdt_counter == `FDT_COUNT)
6658905f 365 begin
d714d3ef 366 if(fdt_elapsed)
7bc95e2e 367 begin
d714d3ef 368 if(negedge_cnt[3:0] == mod_sig_flip) mod_sig_coil <= mod_sig;
7bc95e2e 369 end
6658905f 370 else
7bc95e2e 371 begin
d714d3ef 372 mod_sig_coil <= mod_sig; // just reached fdt. Immediately assign signal to coil
373 end
7bc95e2e 374 end
d714d3ef 375 end
376 else // other modes: don't delay
377 begin
378 mod_sig_coil <= ssp_dout;
379 end
380end
381
382
383
384////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
385// PM3 -> Reader
386// determine the required delay in the mod_sig_buf (set mod_sig_ptr).
387reg temp_buffer_reset;
388
389always @(negedge adc_clk)
390begin
391 if(fdt_reset)
392 begin
393 mod_sig_ptr <= 5'd0;
394 temp_buffer_reset = 1'b0;
395 end
396 else
397 begin
398 if(fdt_counter == `FDT_COUNT && ~fdt_elapsed) // if we just reached fdt
399 if(~(| mod_sig_ptr[4:0]))
400 mod_sig_ptr <= 5'd8; // ... but didn't buffer a 1 yet, delay next 1 by n*128 ticks.
401 else
402 temp_buffer_reset = 1'b1; // else no need for further delays.
403
404 if(negedge_cnt[3:0] == 4'd0) // at rising edge of ssp_clk - ssp_dout changes at the falling edge.
6658905f 405 begin
d714d3ef 406 if((ssp_dout || (| mod_sig_ptr[4:0])) && ~fdt_elapsed) // buffer a 1 (and all subsequent data) until fdt is reached.
407 if (mod_sig_ptr == 5'd31)
408 mod_sig_ptr <= 5'd0; // buffer overflow - data loss.
409 else
410 mod_sig_ptr <= mod_sig_ptr + 1; // increase buffer (= increase delay by 16 adc_clk ticks). mod_sig_ptr always points ahead of first 1.
411 else if(fdt_elapsed && ~temp_buffer_reset)
412 begin
413 // wait for the next 1 after fdt_elapsed before fixing the delay and starting modulation. This ensures that the response can only happen
414 // at intervals of 8 * 16 = 128 adc_clk ticks (as defined in ISO14443-3)
415 if(ssp_dout)
416 temp_buffer_reset = 1'b1;
417 if(mod_sig_ptr == 5'd1)
418 mod_sig_ptr <= 5'd8; // still nothing received, need to go for the next interval
419 else
420 mod_sig_ptr <= mod_sig_ptr - 1; // decrease buffer.
421 end
6658905f 422 end
d714d3ef 423 end
424end
425
426
427
428////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
429// FPGA -> ARM communication:
430// buffer 8 bits data to be sent to ARM. Shift them out bit by bit.
431reg [7:0] to_arm;
432
433always @(negedge adc_clk)
434begin
435 if (negedge_cnt[5:0] == 6'd63) // fill the buffer
7bc95e2e 436 begin
d714d3ef 437 if (mod_type == `SNIFFER)
6658905f 438 begin
d714d3ef 439 if(deep_modulation) // a reader is sending (or there's no field at all)
440 begin
441 to_arm <= {reader_data[3:0], 4'b0000}; // don't send tag data
442 end
443 else
444 begin
445 to_arm <= {reader_data[3:0], tag_data[3:0]};
446 end
6658905f 447 end
448 else
449 begin
d714d3ef 450 to_arm[7:0] <= {mod_sig_ptr[4:0], mod_sig_flip[3:1]}; // feedback timing information
6658905f 451 end
d714d3ef 452 end
d7aa3739 453
d714d3ef 454 if(negedge_cnt[2:0] == 3'b000 && mod_type == `SNIFFER) // shift at double speed
6658905f 455 begin
d714d3ef 456 // Don't shift if we just loaded new data, obviously.
457 if(negedge_cnt[5:0] != 6'd0)
6658905f 458 begin
d714d3ef 459 to_arm[7:1] <= to_arm[6:0];
7bc95e2e 460 end
d714d3ef 461 end
462
463 if(negedge_cnt[3:0] == 4'b0000 && mod_type != `SNIFFER)
464 begin
465 // Don't shift if we just loaded new data, obviously.
466 if(negedge_cnt[6:0] != 7'd0)
7bc95e2e 467 begin
d714d3ef 468 to_arm[7:1] <= to_arm[6:0];
6658905f 469 end
470 end
471
d714d3ef 472end
473
474
475////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
30364d27 476// FPGA <-> ARM communication:
d714d3ef 477// generate a ssp clock and ssp frame signal for the synchronous transfer from/to the ARM
478reg ssp_clk;
479reg ssp_frame;
d714d3ef 480
481always @(negedge adc_clk)
482begin
7bc95e2e 483 if(mod_type == `SNIFFER)
d714d3ef 484 // SNIFFER mode (ssp_clk = adc_clk / 8, ssp_frame clock = adc_clk / 64)):
6658905f 485 begin
d714d3ef 486 if(negedge_cnt[2:0] == 3'd0)
6658905f 487 ssp_clk <= 1'b1;
d714d3ef 488 if(negedge_cnt[2:0] == 3'd4)
489 ssp_clk <= 1'b0;
6658905f 490
d714d3ef 491 if(negedge_cnt[5:0] == 6'd0) // ssp_frame rising edge indicates start of frame
492 ssp_frame <= 1'b1;
493 if(negedge_cnt[5:0] == 6'd8)
494 ssp_frame <= 1'b0;
6658905f 495 end
496 else
e691fc45 497 // all other modes (ssp_clk = adc_clk / 16, ssp_frame clock = adc_clk / 128):
6658905f 498 begin
d714d3ef 499 if(negedge_cnt[3:0] == 4'd0)
500 ssp_clk <= 1'b1;
501 if(negedge_cnt[3:0] == 4'd8)
502 ssp_clk <= 1'b0;
6658905f 503
d714d3ef 504 if(negedge_cnt[6:0] == 7'd7) // ssp_frame rising edge indicates start of frame
505 ssp_frame <= 1'b1;
506 if(negedge_cnt[6:0] == 7'd23)
507 ssp_frame <= 1'b0;
508 end
509end
6658905f 510
d714d3ef 511
512
513////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
514// FPGA -> ARM communication:
515// select the data to be sent to ARM
516reg bit_to_arm;
517reg sendbit;
518
519always @(negedge adc_clk)
520begin
521 if(negedge_cnt[3:0] == 4'd0)
522 begin
523 // What do we communicate to the ARM
524 if(mod_type == `TAGSIM_LISTEN)
525 sendbit = after_hysteresis;
526 else if(mod_type == `TAGSIM_MOD)
527 /* if(fdt_counter > 11'd772) sendbit = mod_sig_coil; // huh?
528 else */
529 sendbit = fdt_indicator;
530 else if (mod_type == `READER_LISTEN)
531 sendbit = curbit;
7bc95e2e 532 else
d714d3ef 533 sendbit = 1'b0;
534 end
6658905f 535
6658905f 536
d714d3ef 537 if(mod_type == `SNIFFER)
538 // send sampled reader and tag data:
539 bit_to_arm = to_arm[7];
540 else if (mod_type == `TAGSIM_MOD && fdt_elapsed && temp_buffer_reset)
541 // send timing information:
542 bit_to_arm = to_arm[7];
543 else
544 // send data or fdt_indicator
545 bit_to_arm = sendbit;
546end
547
548
549
550
551assign ssp_din = bit_to_arm;
e691fc45 552
7bc95e2e 553// Subcarrier (adc_clk/16, for TAGSIM_MOD only).
554wire sub_carrier;
555assign sub_carrier = ~sub_carrier_cnt[3];
e691fc45 556
7bc95e2e 557// in READER_MOD: drop carrier for mod_sig_coil==1 (pause); in READER_LISTEN: carrier always on; in other modes: carrier always off
558assign pwr_hi = (ck_1356megb & (((mod_type == `READER_MOD) & ~mod_sig_coil) || (mod_type == `READER_LISTEN)));
6658905f 559
6658905f 560
e691fc45 561// Enable HF antenna drivers:
6658905f 562assign pwr_oe1 = 1'b0;
e691fc45 563assign pwr_oe3 = 1'b0;
564
7bc95e2e 565// TAGSIM_MOD: short circuit antenna with different resistances (modulated by sub_carrier modulated by mod_sig_coil)
e691fc45 566// for pwr_oe4 = 1 (tristate): antenna load = 10k || 33 = 32,9 Ohms
567// for pwr_oe4 = 0 (active): antenna load = 10k || 33 || 33 = 16,5 Ohms
7554370c 568assign pwr_oe4 = mod_sig_coil & sub_carrier & (mod_type == `TAGSIM_MOD);
6658905f 569
e691fc45 570// This is all LF, so doesn't matter.
571assign pwr_oe2 = 1'b0;
572assign pwr_lo = 1'b0;
6658905f 573
574
575assign dbg = negedge_cnt[3];
576
6658905f 577endmodule
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