diff --git a/armsrc/em4x70.c b/armsrc/em4x70.c
index 68025dcdd..6f962fe40 100644
--- a/armsrc/em4x70.c
+++ b/armsrc/em4x70.c
@@ -30,43 +30,50 @@ static em4x70_tag_t tag = { 0 };
 // EM4170 requires a parity bit on commands, other variants do not.
 static bool command_parity = true;
 
-// Conversion from Ticks to RF periods
-// 1 us = 1.5 ticks
-// 1RF Period = 8us = 12 Ticks
-#define TICKS_PER_FC                        12
 
-// Chip timing from datasheet
-// Converted into Ticks for timing functions
-#define EM4X70_T_TAG_QUARTER_PERIOD          (8 * TICKS_PER_FC)
-#define EM4X70_T_TAG_HALF_PERIOD            (16 * TICKS_PER_FC)
-#define EM4X70_T_TAG_THREE_QUARTER_PERIOD   (24 * TICKS_PER_FC)
-#define EM4X70_T_TAG_FULL_PERIOD            (32 * TICKS_PER_FC) // 1 Bit Period
-#define EM4X70_T_TAG_TWA                   (128 * TICKS_PER_FC) // Write Access Time
-#define EM4X70_T_TAG_DIV                   (224 * TICKS_PER_FC) // Divergency Time
-#define EM4X70_T_TAG_AUTH                 (4224 * TICKS_PER_FC) // Authentication Time
-#define EM4X70_T_TAG_WEE                  (3072 * TICKS_PER_FC) // EEPROM write Time
-#define EM4X70_T_TAG_TWALB                 (672 * TICKS_PER_FC) // Write Access Time of Lock Bits
-#define EM4X70_T_TAG_BITMOD                  (4 * TICKS_PER_FC) // Initial time to stop modulation when sending 0
-#define EM4X70_T_TAG_TOLERANCE               (8 * TICKS_PER_FC) // Tolerance in RF periods for receive/LIW
+#if 1 // Calculation of ticks for timing functions
+    // Conversion from Ticks to RF periods
+    // 1 us = 1.5 ticks
+    // 1RF Period = 8us = 12 Ticks
+    #define TICKS_PER_FC                        12
 
-#define EM4X70_T_TAG_TIMEOUT                 (4 * EM4X70_T_TAG_FULL_PERIOD) // Timeout if we ever get a pulse longer than this
-#define EM4X70_T_WAITING_FOR_LIW             50 // Pulses to wait for listen window
-#define EM4X70_T_READ_HEADER_LEN             16 // Read header length (16 bit periods)
+    // Chip timing from datasheet
+    // Converted into Ticks for timing functions
+    #define EM4X70_T_TAG_QUARTER_PERIOD          (8 * TICKS_PER_FC)
+    #define EM4X70_T_TAG_HALF_PERIOD            (16 * TICKS_PER_FC)
+    #define EM4X70_T_TAG_THREE_QUARTER_PERIOD   (24 * TICKS_PER_FC)
+    #define EM4X70_T_TAG_FULL_PERIOD            (32 * TICKS_PER_FC) // 1 Bit Period
+    #define EM4X70_T_TAG_TWA                   (128 * TICKS_PER_FC) // Write Access Time
+    #define EM4X70_T_TAG_DIV                   (224 * TICKS_PER_FC) // Divergency Time
+    #define EM4X70_T_TAG_AUTH                 (4224 * TICKS_PER_FC) // Authentication Time
+    #define EM4X70_T_TAG_WEE                  (3072 * TICKS_PER_FC) // EEPROM write Time
+    #define EM4X70_T_TAG_TWALB                 (672 * TICKS_PER_FC) // Write Access Time of Lock Bits
+    #define EM4X70_T_TAG_BITMOD                  (4 * TICKS_PER_FC) // Initial time to stop modulation when sending 0
+    #define EM4X70_T_TAG_TOLERANCE               (8 * TICKS_PER_FC) // Tolerance in RF periods for receive/LIW
 
-#define EM4X70_COMMAND_RETRIES               5 // Attempts to send/read command
-#define EM4X70_MAX_RECEIVE_LENGTH           96 // Maximum bits to expect from any command
+    #define EM4X70_T_TAG_TIMEOUT                 (4 * EM4X70_T_TAG_FULL_PERIOD) // Timeout if we ever get a pulse longer than this
+    #define EM4X70_T_WAITING_FOR_LIW             50 // Pulses to wait for listen window
+    #define EM4X70_T_READ_HEADER_LEN             16 // Read header length (16 bit periods)
 
-/**
- * These IDs are from the EM4170 datasheet
- * Some versions of the chip require a
- * (even) parity bit, others do not
- */
-#define EM4X70_COMMAND_ID                   0x01
-#define EM4X70_COMMAND_UM1                  0x02
-#define EM4X70_COMMAND_AUTH                 0x03
-#define EM4X70_COMMAND_PIN                  0x04
-#define EM4X70_COMMAND_WRITE                0x05
-#define EM4X70_COMMAND_UM2                  0x07
+    #define EM4X70_COMMAND_RETRIES               5 // Attempts to send/read command
+    #define EM4X70_MAX_RECEIVE_LENGTH           96 // Maximum bits to expect from any command
+#endif // Calculation of ticks for timing functions
+
+#if 1 // EM4x70 Command IDs
+    /**
+     * These IDs are from the EM4170 datasheet.
+     * Some versions of the chip require a
+     * (even) parity bit, others do not.
+     * The command is thus stored only in the
+     * three least significant bits (mask 0x07).
+     */
+    #define EM4X70_COMMAND_ID                   0x01
+    #define EM4X70_COMMAND_UM1                  0x02
+    #define EM4X70_COMMAND_AUTH                 0x03
+    #define EM4X70_COMMAND_PIN                  0x04
+    #define EM4X70_COMMAND_WRITE                0x05
+    #define EM4X70_COMMAND_UM2                  0x07
+#endif // EM4x70 Command IDs
 
 // Constants used to determine high/low state of signal
 #define EM4X70_NOISE_THRESHOLD  13  // May depend on noise in environment