diff --git a/SerialPort.cpp b/SerialPort.cpp
index 27618e5..c8ca4b1 100644
--- a/SerialPort.cpp
+++ b/SerialPort.cpp
@@ -343,6 +343,24 @@ void SerialPort::process()
 #endif
                     break;
 
+                case CMD_DMR_CACH_AT_CTRL:
+#if defined(DUPLEX)
+                    if (m_dmrEnable) {
+                        err = RSN_INVALID_REQUEST;
+                        if (m_len == 4U) {
+                            dmrTX.setIgnoreCACH_AT(m_buffer[3U]);
+                            err = RSN_OK;
+                        }
+                    }
+                    if (err != RSN_OK) {
+                        DEBUG2("SerialPort: process(): received invalid DMR CACH AT Control", err);
+                        sendNAK(err);
+                    }
+#else
+                    sendNAK(RSN_INVALID_REQUEST);
+#endif
+                    break;
+
                 /** Project 25 */
                 case CMD_P25_DATA:
                     if (m_p25Enable) {
diff --git a/SerialPort.h b/SerialPort.h
index 93289c7..9ed80b9 100644
--- a/SerialPort.h
+++ b/SerialPort.h
@@ -90,6 +90,7 @@ enum DVM_COMMANDS {
     CMD_DMR_SHORTLC = 0x1CU,
     CMD_DMR_START = 0x1DU,
     CMD_DMR_ABORT = 0x1EU,
+    CMD_DMR_CACH_AT_CTRL = 0x1FU,
 
     CMD_P25_DATA = 0x31U,
     CMD_P25_LOST = 0x32U,
diff --git a/dmr/DMRTX.cpp b/dmr/DMRTX.cpp
index 561b0c4..c58d252 100644
--- a/dmr/DMRTX.cpp
+++ b/dmr/DMRTX.cpp
@@ -14,7 +14,7 @@
 *   Copyright (C) 2009-2017 by Jonathan Naylor G4KLX
 *   Copyright (C) 2016 by Colin Durbridge G4EML
 *   Copyright (C) 2017 by Andy Uribe CA6JAU
-*   Copyright (C) 2021 by Bryan Biedenkapp N2PLL
+*   Copyright (C) 2021-2022 by Bryan Biedenkapp N2PLL
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
@@ -81,6 +81,7 @@ DMRTX::DMRTX() :
     m_frameCount(0U),
     m_abortCount(),
     m_abort(),
+    m_cachATControl(0U),
     m_controlPrev(MARK_NONE)
 {
     ::memcpy(m_newShortLC, EMPTY_SHORT_LC, 12U);
@@ -306,6 +307,18 @@ uint8_t DMRTX::getSpace2() const
     return m_fifo[1U].getSpace() / (DMR_FRAME_LENGTH_BYTES + 2U);
 }
 
+/// <summary>
+/// Sets the ignore flags for setting the CACH Access Type bit.
+/// </summary>
+/// <param name="slot"></param>
+void DMRTX::setIgnoreCACH_AT(uint8_t slot)
+{
+    m_cachATControl = slot;
+    if (m_cachATControl > 3U) {
+        m_cachATControl = 0U;
+    }
+}
+
 /// <summary>
 /// Sets the DMR color code.
 /// </summary>
@@ -441,8 +454,16 @@ void DMRTX::createCACH(uint8_t txSlotIndex, uint8_t rxSlotIndex)
     m_markBuffer[2U] = rxSlotIndex == 1U ? MARK_SLOT1 : MARK_SLOT2;
 
     bool at = false;
-    if (m_frameCount >= STARTUP_COUNT)
-        at = m_fifo[rxSlotIndex].getData() > 0U;
+    if (m_frameCount >= STARTUP_COUNT) {
+        if (m_cachATControl == 0U) {
+            at = m_fifo[rxSlotIndex].getData() > 0U;
+        } else {
+            if (m_cachATControl != 3U && m_cachATControl != (rxSlotIndex + 1U)) {
+                at = m_fifo[rxSlotIndex].getData() > 0U;
+            }
+        }
+    }
+
     bool tc = txSlotIndex == 1U;
     bool ls0 = true;            // For 1 and 2
     bool ls1 = true;
diff --git a/dmr/DMRTX.h b/dmr/DMRTX.h
index 70daf8c..baf6d71 100644
--- a/dmr/DMRTX.h
+++ b/dmr/DMRTX.h
@@ -14,7 +14,7 @@
 *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
 *   Copyright (C) 2016 by Colin Durbridge G4EML
 *   Copyright (C) 2017 by Andy Uribe CA6JAU
-*   Copyright (C) 2021 by Bryan Biedenkapp N2PLL
+*   Copyright (C) 2021-2022 by Bryan Biedenkapp N2PLL
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
@@ -85,6 +85,8 @@ namespace dmr
         /// <summary>Helper to get how much space the slot 2 ring buffer has for samples.</summary>
         uint8_t getSpace2() const;
 
+        /// <summary>Sets the ignore flags for setting the CACH Access Type bit.</summary>
+        void setIgnoreCACH_AT(uint8_t slot);
         /// <summary>Sets the DMR color code.</summary>
         void setColorCode(uint8_t colorCode);
 
@@ -117,6 +119,8 @@ namespace dmr
         uint32_t m_abortCount[2U];
         bool m_abort[2U];
 
+        uint8_t m_cachATControl;
+
         uint8_t m_controlPrev;
 
         /// <summary></summary>