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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;
115// convert to signed signals (and multiply by two for samples at t-4 and t)
116wire signed [10:0] input_prev_4_times_2 = {0, 0, input_prev_4, 0};
117wire signed [10:0] input_prev_3_times_1 = {0, 0, 0, input_prev_3};
118wire signed [10:0] input_prev_1_times_1 = {0, 0, 0, input_prev_1};
119wire signed [10:0] adc_d_times_2 = {0, 0, adc_d, 0};
6658905f 120
d714d3ef 121wire signed [10:0] tmp_1, tmp_2;
122wire signed [10:0] adc_d_filtered;
123integer i;
6658905f 124
d714d3ef 125assign tmp_1 = input_prev_4_times_2 + input_prev_3_times_1;
126assign tmp_2 = input_prev_1_times_1 + adc_d_times_2;
127
6658905f 128always @(negedge adc_clk)
129begin
d714d3ef 130 // for (i = 3; i > 0; i = i - 1)
131 // begin
132 // input_shift[i] <= input_shift[i-1];
133 // end
134 // input_shift[0] <= adc_d;
135 input_prev_4 <= input_prev_3;
136 input_prev_3 <= input_prev_2;
137 input_prev_2 <= input_prev_1;
138 input_prev_1 <= adc_d;
139end
140
141// assign adc_d_filtered = (input_shift[3] << 1) + input_shift[2] - input_shift[0] - (adc_d << 1);
142assign adc_d_filtered = tmp_1 - tmp_2;
143
6658905f 144
d714d3ef 145////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
146// internal FPGA timing. Maximum required period is 128 carrier clock cycles for a full 8 Bit transfer to ARM. (i.e. we need a
147// 7 bit counter). Adjust its frequency to external reader's clock when simulating a tag or sniffing.
148reg pre_after_hysteresis;
149reg [3:0] reader_falling_edge_time;
150reg [6:0] negedge_cnt;
151
152always @(negedge adc_clk)
153begin
154 // detect a reader signal's falling edge and remember its timing:
155 pre_after_hysteresis <= after_hysteresis;
156 if (pre_after_hysteresis && ~after_hysteresis)
157 begin
158 reader_falling_edge_time[3:0] <= negedge_cnt[3:0];
159 end
160
161 // adjust internal timer counter if necessary:
162 if (negedge_cnt[3:0] == 4'd13 && (mod_type == `SNIFFER || mod_type == `TAGSIM_LISTEN) && deep_modulation)
6658905f 163 begin
d714d3ef 164 if (reader_falling_edge_time == 4'd1) // reader signal changes right after sampling. Better sample earlier next time.
6658905f 165 begin
d714d3ef 166 negedge_cnt <= negedge_cnt + 2; // time warp
167 end
168 else if (reader_falling_edge_time == 4'd0) // reader signal changes right before sampling. Better sample later next time.
169 begin
170 negedge_cnt <= negedge_cnt; // freeze time
6658905f 171 end
172 else
173 begin
d714d3ef 174 negedge_cnt <= negedge_cnt + 1; // Continue as usual
6658905f 175 end
d714d3ef 176 reader_falling_edge_time[3:0] <= 4'd8; // adjust only once per detected edge
6658905f 177 end
d714d3ef 178 else if (negedge_cnt == 7'd127) // normal operation: count from 0 to 127
6658905f 179 begin
d714d3ef 180 negedge_cnt <= 0;
7bc95e2e 181 end
d714d3ef 182 else
183 begin
184 negedge_cnt <= negedge_cnt + 1;
185 end
186end
7bc95e2e 187
d714d3ef 188
189////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
190// Tag -> PM3:
191// determine best possible time for starting/resetting the modulation detector.
192reg [3:0] mod_detect_reset_time;
193
194always @(negedge adc_clk)
195begin
196 if (mod_type == `READER_LISTEN)
197 // (our) reader signal changes at t=1, tag response expected n*16+4 ticks later, further delayed by
198 // 3 ticks ADC conversion.
199 // 1 + 4 + 3 = 8
7bc95e2e 200 begin
d714d3ef 201 mod_detect_reset_time <= 4'd8;
202 end
203 else
204 if (mod_type == `SNIFFER)
205 begin
206 // detect a rising edge of reader's signal and sync modulation detector to the tag's answer:
207 if (~pre_after_hysteresis && after_hysteresis && deep_modulation)
208 // reader signal rising edge detected at negedge_cnt[3:0]. This signal had been delayed
209 // 9 ticks by the RF part + 3 ticks by the A/D converter + 1 tick to assign to after_hysteresis.
210 // The tag will respond n*16 + 4 ticks later + 3 ticks A/D converter delay.
211 // - 9 - 3 - 1 + 4 + 3 = -6
e691fc45 212 begin
d714d3ef 213 mod_detect_reset_time <= negedge_cnt[3:0] - 4'd4;
e691fc45 214 end
7bc95e2e 215 end
d714d3ef 216end
217
218
219////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
220// Tag -> PM3:
221// modulation detector. Looks for the steepest falling and rising edges within a 16 clock period. If there is both a significant
222// falling and rising edge (in any order), a modulation is detected.
223reg signed [10:0] rx_mod_falling_edge_max;
224reg signed [10:0] rx_mod_rising_edge_max;
225reg curbit;
226
227always @(negedge adc_clk)
228begin
229 if(negedge_cnt[3:0] == mod_detect_reset_time)
230 begin
231 // detect modulation signal: if modulating, there must have been a falling AND a rising edge
232 if (rx_mod_falling_edge_max > 5 && rx_mod_rising_edge_max > 5)
233 curbit <= 1'b1; // modulation
234 else
235 curbit <= 1'b0; // no modulation
236 // reset modulation detector
237 rx_mod_rising_edge_max <= 0;
238 rx_mod_falling_edge_max <= 0;
239 end
240 else // look for steepest edges (slopes)
7bc95e2e 241 begin
242 if (adc_d_filtered > 0)
243 begin
244 if (adc_d_filtered > rx_mod_falling_edge_max)
245 rx_mod_falling_edge_max <= adc_d_filtered;
246 end
247 else
248 begin
249 if (-adc_d_filtered > rx_mod_rising_edge_max)
250 rx_mod_rising_edge_max <= -adc_d_filtered;
251 end
252 end
253
d714d3ef 254end
255
e691fc45 256
e691fc45 257
d714d3ef 258////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
259// Tag+Reader -> PM3
260// sample 4 bits reader data and 4 bits tag data for sniffing
261reg [3:0] reader_data;
262reg [3:0] tag_data;
263
264always @(negedge adc_clk)
265begin
266 if(negedge_cnt[3:0] == 4'd0)
6658905f 267 begin
d714d3ef 268 reader_data[3:0] <= {reader_data[2:0], after_hysteresis};
269 tag_data[3:0] <= {tag_data[2:0], curbit};
270 end
271end
272
7bc95e2e 273
274
d714d3ef 275////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
276// PM3 -> Tag:
277// a delay line to ensure that we send the (emulated) tag's answer at the correct time according to ISO14443-3
278reg [31:0] mod_sig_buf;
279reg [4:0] mod_sig_ptr;
280reg mod_sig;
281
282always @(negedge adc_clk)
283begin
284 if(negedge_cnt[3:0] == 4'd0) // sample data at rising edge of ssp_clk - ssp_dout changes at the falling edge.
7bc95e2e 285 begin
d714d3ef 286 mod_sig_buf[31:2] <= mod_sig_buf[30:1]; // shift
287 if (~ssp_dout && ~mod_sig_buf[1])
288 mod_sig_buf[1] <= 1'b0; // delete the correction bit (a single 1 preceded and succeeded by 0)
7bc95e2e 289 else
d714d3ef 290 mod_sig_buf[1] <= mod_sig_buf[0];
291 mod_sig_buf[0] <= ssp_dout; // add new data to the delay line
292
293 mod_sig = mod_sig_buf[mod_sig_ptr]; // the delayed signal.
7bc95e2e 294 end
d714d3ef 295end
7bc95e2e 296
d7aa3739 297
298
d714d3ef 299////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
300// PM3 -> Tag, internal timing:
301// a timer for the 1172 cycles fdt (Frame Delay Time). Start the timer with a rising edge of the reader's signal.
302// set fdt_elapsed when we no longer need to delay data. Set fdt_indicator when we can start sending data.
303// Note: the FPGA only takes care for the 1172 delay. To achieve an additional 1236-1172=64 ticks delay, the ARM must send
304// a correction bit (before the start bit). The correction bit will be coded as 00010000, i.e. it adds 4 bits to the
305// transmission stream, causing the required additional delay.
306reg [10:0] fdt_counter;
307reg fdt_indicator, fdt_elapsed;
308reg [3:0] mod_sig_flip;
309reg [3:0] sub_carrier_cnt;
d7aa3739 310
d714d3ef 311// we want to achieve a delay of 1172. The RF part already has delayed the reader signals's rising edge
312// 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
313// count to 1172 - 9 - 3 - 32 = 1128
314`define FDT_COUNT 11'd1128
d7aa3739 315
d714d3ef 316// The ARM must not send too early, otherwise the mod_sig_buf will overflow, therefore signal that we are ready
317// 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.
318// fdt_indicator could appear at ssp_din after 1 tick, the transfer needs 16 ticks, the ARM can send 128 ticks later.
319// 1128 - 464 - 1 - 128 - 8 = 535
320`define FDT_INDICATOR_COUNT 11'd535
d7aa3739 321
d714d3ef 322// reset on a pause in listen mode. I.e. the counter starts when the pause is over:
323assign fdt_reset = ~after_hysteresis && mod_type == `TAGSIM_LISTEN;
324
325always @(negedge adc_clk)
326begin
327 if (fdt_reset)
d7aa3739 328 begin
d714d3ef 329 fdt_counter <= 11'd0;
330 fdt_elapsed <= 1'b0;
331 fdt_indicator <= 1'b0;
332 end
333 else
334 begin
335 if(fdt_counter == `FDT_COUNT)
336 begin
337 if(~fdt_elapsed) // just reached fdt.
338 begin
339 mod_sig_flip <= negedge_cnt[3:0]; // start modulation at this time
340 sub_carrier_cnt <= 4'd0; // subcarrier phase in sync with start of modulation
341 fdt_elapsed <= 1'b1;
342 end
343 else
344 begin
345 sub_carrier_cnt <= sub_carrier_cnt + 1;
346 end
d7aa3739 347 end
d7aa3739 348 else
349 begin
d714d3ef 350 fdt_counter <= fdt_counter + 1;
d7aa3739 351 end
d7aa3739 352 end
353
d714d3ef 354 if(fdt_counter == `FDT_INDICATOR_COUNT) fdt_indicator <= 1'b1;
355end
356
d7aa3739 357
d714d3ef 358////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
359// PM3 -> Reader or Tag
360// assign a modulation signal to the antenna. This signal is either a delayed signal (to achieve fdt when sending to a reader)
361// or undelayed when sending to a tag
362reg mod_sig_coil;
d7aa3739 363
d714d3ef 364always @(negedge adc_clk)
365begin
366 if (mod_type == `TAGSIM_MOD) // need to take care of proper fdt timing
7bc95e2e 367 begin
d714d3ef 368 if(fdt_counter == `FDT_COUNT)
6658905f 369 begin
d714d3ef 370 if(fdt_elapsed)
7bc95e2e 371 begin
d714d3ef 372 if(negedge_cnt[3:0] == mod_sig_flip) mod_sig_coil <= mod_sig;
7bc95e2e 373 end
6658905f 374 else
7bc95e2e 375 begin
d714d3ef 376 mod_sig_coil <= mod_sig; // just reached fdt. Immediately assign signal to coil
377 end
7bc95e2e 378 end
d714d3ef 379 end
380 else // other modes: don't delay
381 begin
382 mod_sig_coil <= ssp_dout;
383 end
384end
385
386
387
388////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
389// PM3 -> Reader
390// determine the required delay in the mod_sig_buf (set mod_sig_ptr).
391reg temp_buffer_reset;
392
393always @(negedge adc_clk)
394begin
395 if(fdt_reset)
396 begin
397 mod_sig_ptr <= 5'd0;
398 temp_buffer_reset = 1'b0;
399 end
400 else
401 begin
402 if(fdt_counter == `FDT_COUNT && ~fdt_elapsed) // if we just reached fdt
403 if(~(| mod_sig_ptr[4:0]))
404 mod_sig_ptr <= 5'd8; // ... but didn't buffer a 1 yet, delay next 1 by n*128 ticks.
405 else
406 temp_buffer_reset = 1'b1; // else no need for further delays.
407
408 if(negedge_cnt[3:0] == 4'd0) // at rising edge of ssp_clk - ssp_dout changes at the falling edge.
6658905f 409 begin
d714d3ef 410 if((ssp_dout || (| mod_sig_ptr[4:0])) && ~fdt_elapsed) // buffer a 1 (and all subsequent data) until fdt is reached.
411 if (mod_sig_ptr == 5'd31)
412 mod_sig_ptr <= 5'd0; // buffer overflow - data loss.
413 else
414 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.
415 else if(fdt_elapsed && ~temp_buffer_reset)
416 begin
417 // wait for the next 1 after fdt_elapsed before fixing the delay and starting modulation. This ensures that the response can only happen
418 // at intervals of 8 * 16 = 128 adc_clk ticks (as defined in ISO14443-3)
419 if(ssp_dout)
420 temp_buffer_reset = 1'b1;
421 if(mod_sig_ptr == 5'd1)
422 mod_sig_ptr <= 5'd8; // still nothing received, need to go for the next interval
423 else
424 mod_sig_ptr <= mod_sig_ptr - 1; // decrease buffer.
425 end
6658905f 426 end
d714d3ef 427 end
428end
429
430
431
432////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
433// FPGA -> ARM communication:
434// buffer 8 bits data to be sent to ARM. Shift them out bit by bit.
435reg [7:0] to_arm;
436
437always @(negedge adc_clk)
438begin
439 if (negedge_cnt[5:0] == 6'd63) // fill the buffer
7bc95e2e 440 begin
d714d3ef 441 if (mod_type == `SNIFFER)
6658905f 442 begin
d714d3ef 443 if(deep_modulation) // a reader is sending (or there's no field at all)
444 begin
445 to_arm <= {reader_data[3:0], 4'b0000}; // don't send tag data
446 end
447 else
448 begin
449 to_arm <= {reader_data[3:0], tag_data[3:0]};
450 end
6658905f 451 end
452 else
453 begin
d714d3ef 454 to_arm[7:0] <= {mod_sig_ptr[4:0], mod_sig_flip[3:1]}; // feedback timing information
6658905f 455 end
d714d3ef 456 end
d7aa3739 457
d714d3ef 458 if(negedge_cnt[2:0] == 3'b000 && mod_type == `SNIFFER) // shift at double speed
6658905f 459 begin
d714d3ef 460 // Don't shift if we just loaded new data, obviously.
461 if(negedge_cnt[5:0] != 6'd0)
6658905f 462 begin
d714d3ef 463 to_arm[7:1] <= to_arm[6:0];
7bc95e2e 464 end
d714d3ef 465 end
466
467 if(negedge_cnt[3:0] == 4'b0000 && mod_type != `SNIFFER)
468 begin
469 // Don't shift if we just loaded new data, obviously.
470 if(negedge_cnt[6:0] != 7'd0)
7bc95e2e 471 begin
d714d3ef 472 to_arm[7:1] <= to_arm[6:0];
6658905f 473 end
474 end
475
d714d3ef 476end
477
478
479////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
480// FPGA -> ARM communication:
481// generate a ssp clock and ssp frame signal for the synchronous transfer from/to the ARM
482reg ssp_clk;
483reg ssp_frame;
484reg [2:0] ssp_frame_counter;
485
486always @(negedge adc_clk)
487begin
7bc95e2e 488 if(mod_type == `SNIFFER)
d714d3ef 489 // SNIFFER mode (ssp_clk = adc_clk / 8, ssp_frame clock = adc_clk / 64)):
6658905f 490 begin
d714d3ef 491 if(negedge_cnt[2:0] == 3'd0)
6658905f 492 ssp_clk <= 1'b1;
d714d3ef 493 if(negedge_cnt[2:0] == 3'd4)
494 ssp_clk <= 1'b0;
6658905f 495
d714d3ef 496 if(negedge_cnt[5:0] == 6'd0) // ssp_frame rising edge indicates start of frame
497 ssp_frame <= 1'b1;
498 if(negedge_cnt[5:0] == 6'd8)
499 ssp_frame <= 1'b0;
6658905f 500 end
501 else
e691fc45 502 // all other modes (ssp_clk = adc_clk / 16, ssp_frame clock = adc_clk / 128):
6658905f 503 begin
d714d3ef 504 if(negedge_cnt[3:0] == 4'd0)
505 ssp_clk <= 1'b1;
506 if(negedge_cnt[3:0] == 4'd8)
507 ssp_clk <= 1'b0;
6658905f 508
d714d3ef 509 if(negedge_cnt[6:0] == 7'd7) // ssp_frame rising edge indicates start of frame
510 ssp_frame <= 1'b1;
511 if(negedge_cnt[6:0] == 7'd23)
512 ssp_frame <= 1'b0;
513 end
514end
6658905f 515
d714d3ef 516
517
518////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
519// FPGA -> ARM communication:
520// select the data to be sent to ARM
521reg bit_to_arm;
522reg sendbit;
523
524always @(negedge adc_clk)
525begin
526 if(negedge_cnt[3:0] == 4'd0)
527 begin
528 // What do we communicate to the ARM
529 if(mod_type == `TAGSIM_LISTEN)
530 sendbit = after_hysteresis;
531 else if(mod_type == `TAGSIM_MOD)
532 /* if(fdt_counter > 11'd772) sendbit = mod_sig_coil; // huh?
533 else */
534 sendbit = fdt_indicator;
535 else if (mod_type == `READER_LISTEN)
536 sendbit = curbit;
7bc95e2e 537 else
d714d3ef 538 sendbit = 1'b0;
539 end
6658905f 540
6658905f 541
d714d3ef 542 if(mod_type == `SNIFFER)
543 // send sampled reader and tag data:
544 bit_to_arm = to_arm[7];
545 else if (mod_type == `TAGSIM_MOD && fdt_elapsed && temp_buffer_reset)
546 // send timing information:
547 bit_to_arm = to_arm[7];
548 else
549 // send data or fdt_indicator
550 bit_to_arm = sendbit;
551end
552
553
554
555
556assign ssp_din = bit_to_arm;
e691fc45 557
7bc95e2e 558// Subcarrier (adc_clk/16, for TAGSIM_MOD only).
559wire sub_carrier;
560assign sub_carrier = ~sub_carrier_cnt[3];
e691fc45 561
7bc95e2e 562// in READER_MOD: drop carrier for mod_sig_coil==1 (pause); in READER_LISTEN: carrier always on; in other modes: carrier always off
563assign pwr_hi = (ck_1356megb & (((mod_type == `READER_MOD) & ~mod_sig_coil) || (mod_type == `READER_LISTEN)));
6658905f 564
6658905f 565
e691fc45 566// Enable HF antenna drivers:
6658905f 567assign pwr_oe1 = 1'b0;
e691fc45 568assign pwr_oe3 = 1'b0;
569
7bc95e2e 570// TAGSIM_MOD: short circuit antenna with different resistances (modulated by sub_carrier modulated by mod_sig_coil)
e691fc45 571// for pwr_oe4 = 1 (tristate): antenna load = 10k || 33 = 32,9 Ohms
572// for pwr_oe4 = 0 (active): antenna load = 10k || 33 || 33 = 16,5 Ohms
7bc95e2e 573assign pwr_oe4 = ~(mod_sig_coil & sub_carrier & (mod_type == `TAGSIM_MOD));
6658905f 574
e691fc45 575// This is all LF, so doesn't matter.
576assign pwr_oe2 = 1'b0;
577assign pwr_lo = 1'b0;
6658905f 578
579
580assign dbg = negedge_cnt[3];
581
6658905f 582endmodule
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