diff --git a/src/hei_user_interface.hpp b/src/hei_user_interface.hpp
index 09cbcfb..58f5e34 100644
--- a/src/hei_user_interface.hpp
+++ b/src/hei_user_interface.hpp
@@ -11,6 +11,7 @@
 #include <stdlib.h>
 
 #include <hei_chip.hpp>
+#include <hei_types.hpp>
 
 namespace libhei
 {
@@ -22,30 +23,27 @@
  *                   the isolator by the user application via the isolator main
  *                   APIs.
  *
- * @param o_buffer   Allocated memory space for the returned contents of the
- *                   register.
- *
- * @param io_bufSize The input parameter is the maximum size of the allocated
- *                   o_buffer. The return value is the number of bytes actually
- *                   written to the buffer.
- *
  * @param i_regType  The user application may support different types of
  *                   registers. This value is provided to the isolator by the
  *                   user application via the Chip Data Files. The user
  *                   application is responsible for knowing what to do with this
  *                   parameter.
  *
- * @param i_address  The register address. The values is a 1, 2, 4, or 8 byte
- *                   address (right justified), which is provided to the
- *                   isolator by the user application via the Chip Data Files.
+ * @param i_address  The register address, which is provided to the isolator by
+ *                   the user application via the Chip Data Files. This is a 1,
+ *                   2, 4, or 8 byte value (right justified) as defined by the
+ *                   register type.
+ *
+ * @param o_value    The returned register value. This is a 1, 2, 4, or 8 byte
+ *                   value (right justified) as defined by the register type.
  *
  * @return false => register access was successful
  *         true  => hardware access failure
  *         Note that in the case of a failure, the user application is
  *         responsible for reporting why the register access failed.
  */
-bool registerRead(const Chip& i_chip, void* o_buffer, size_t& io_bufSize,
-                  uint64_t i_regType, uint64_t i_address);
+bool registerRead(const Chip& i_chip, RegisterType_t i_regType,
+                  uint64_t i_address, uint64_t& o_value);
 
 #ifdef __HEI_ENABLE_HW_WRITE
 
@@ -56,30 +54,27 @@
  *                   the isolator by the user application via the isolator main
  *                   APIs.
  *
- * @param i_buffer   Allocated memory space containing the register contents to
- *                   write to hardware.
- *
- * @param io_bufSize The input parameter is the number of byte from i_buffer to
- *                   write to the hardware register. The return value is the
- *                   actual number of bytes written to the hardware register.
- *
  * @param i_regType  The user application may support different types of
  *                   registers. This value is provided to the isolator by the
  *                   user application via the Chip Data Files. The user
  *                   application is responsible for knowing what to do with this
  *                   parameter.
  *
- * @param i_address  The register address. The values is a 1, 2, 4, or 8 byte
- *                   address (right justified), which is provided to the
- *                   isolator by the user application via the Chip Data Files.
+ * @param i_address  The register address, which is provided to the isolator by
+ *                   the user application via the Chip Data Files. This is a 1,
+ *                   2, 4, or 8 byte value (right justified) as defined by the
+ *                   register type.
+ *
+ * @param i_value    The register value to write. This is a 1, 2, 4, or 8 byte
+ *                   value (right justified) as defined by the register type.
  *
  * @return false => register access was successful
  *         true  => hardware access failure
  *         Note that in the case of a failure, the user application is
  *         responsible for reporting why the register access failed.
  */
-bool registerWrite(const Chip& i_chip, void* i_buffer, size_t& io_bufSize,
-                   uint64_t i_regType, uint64_t i_address);
+bool registerWrite(const Chip& i_chip, RegisterType_t i_regType,
+                   uint64_t i_address, uint64_t i_value);
 
 #endif // __HEI_ENABLE_HW_WRITE
 
diff --git a/src/register/hei_hardware_register.cpp b/src/register/hei_hardware_register.cpp
index 2d2167e..d24d251 100644
--- a/src/register/hei_hardware_register.cpp
+++ b/src/register/hei_hardware_register.cpp
@@ -52,33 +52,23 @@
 {
     bool accessFailure = false;
 
+    // This register must be readable.
+    HEI_ASSERT(queryAttrFlag(REG_ATTR_ACCESS_READ));
+
     // Read from hardware only if the read is forced or the entry for this
     // instance does not exist in the cache.
     if (i_force || !queryCache(i_chip))
     {
-        // This register must be readable.
-        HEI_ASSERT(queryAttrFlag(REG_ATTR_ACCESS_READ));
-
-        // Get the buffer from the register cache.
-        BitString& bs = accessCache(i_chip);
-
-        // Get the byte size of the buffer.
-        size_t sz_buffer = BitString::getMinBytes(bs.getBitLen());
-
         // Read this register from hardware.
-        accessFailure = registerRead(i_chip, bs.getBufAddr(), sz_buffer,
-                                     getType(), getAddress());
-        if (accessFailure)
+        uint64_t val  = 0;
+        accessFailure = registerRead(i_chip, getType(), getAddress(), val);
+        if (!accessFailure)
         {
-            // The read failed and we can't trust what was put in the register
-            // cache. So remove this instance's entry from the cache.
-            flush(i_chip);
-        }
-        else
-        {
-            // Sanity check. The returned size of the data written to the buffer
-            // should match the register size.
-            HEI_ASSERT(getSize() == sz_buffer);
+            // Get the buffer from the register cache.
+            BitString& bs = accessCache(i_chip);
+
+            // Set this value in the bit string buffer.
+            bs.setFieldRight(0, bs.getBitLen(), val);
         }
     }
 
@@ -91,8 +81,6 @@
 
 bool HardwareRegister::write(const Chip& i_chip) const
 {
-    bool accessFailure = false;
-
     // This register must be writable.
     HEI_ASSERT(queryAttrFlag(REG_ATTR_ACCESS_WRITE));
 
@@ -102,21 +90,11 @@
     // Get the buffer from the register cache.
     BitString& bs = accessCache(i_chip);
 
-    // Get the byte size of the buffer.
-    size_t sz_buffer = BitString::getMinBytes(bs.getBitLen());
+    // Set this value from the bit string buffer.
+    uint64_t val = bs.getFieldRight(0, bs.getBitLen());
 
     // Write to this register to hardware.
-    accessFailure = registerWrite(i_chip, bs.getBufAddr(), sz_buffer, getType(),
-                                  getAddress());
-
-    if (accessFailure)
-    {
-        // Sanity check. The returned size of the data written to the buffer
-        // should match the register size.
-        HEI_ASSERT(getSize() == sz_buffer);
-    }
-
-    return accessFailure;
+    return registerWrite(i_chip, getType(), getAddress(), val);
 }
 
 #endif // __HEI_ENABLE_HW_WRITE
diff --git a/test/simulator/sim_hardware_access.cpp b/test/simulator/sim_hardware_access.cpp
index e8c45ad..d0625cc 100644
--- a/test/simulator/sim_hardware_access.cpp
+++ b/test/simulator/sim_hardware_access.cpp
@@ -15,44 +15,26 @@
 
 //------------------------------------------------------------------------------
 
-bool registerRead(const Chip& i_chip, void* o_buffer, size_t& io_bufSize,
-                  uint64_t i_regType, uint64_t i_address)
+bool registerRead(const Chip& i_chip, RegisterType_t i_regType,
+                  uint64_t i_address, uint64_t& o_value)
 {
     bool accessFailure = false;
 
-    HEI_ASSERT(nullptr != o_buffer);
-    HEI_ASSERT(0 != io_bufSize);
-
-    // Get access to data through the singleton
+    // Get access to data through the singleton.
     SimulatorData& theSimData = SimulatorData::getSingleton();
 
     switch (i_regType)
     {
         case REG_TYPE_SCOM:
-        {
-            // Get the register value and change its endianness
-            uint64_t regValue =
-                htobe64(theSimData.getScomReg(i_chip, (uint32_t)i_address));
-            // Get size of register value for calling code and memcopy
-            io_bufSize = sizeof(regValue);
-            memcpy(o_buffer, &regValue, io_bufSize);
+            o_value = theSimData.getScomReg(i_chip, (uint32_t)i_address);
             break;
-        }
         case REG_TYPE_ID_SCOM:
-        {
-            // Get the register value and change its endianness
-            uint64_t regValue =
-                htobe64(theSimData.getIdScomReg(i_chip, i_address));
-            // Get size of register value for calling code and memcopy
-            io_bufSize = sizeof(regValue);
-            memcpy(o_buffer, &regValue, io_bufSize);
+            o_value = theSimData.getIdScomReg(i_chip, i_address);
             break;
-        }
         default:
             accessFailure = true;
-            HEI_ERR("registerRead(%p,%p,%" PRIu64 ",%" PRIx64 ",%" PRIx64 ")",
-                    i_chip.getChip(), o_buffer, (uint64_t)io_bufSize, i_regType,
-                    i_address);
+            HEI_ERR("registerRead(%p,%" PRIu8 ",%" PRIx64 ")", i_chip.getChip(),
+                    i_regType, i_address);
     }
 
     return accessFailure;
@@ -62,22 +44,18 @@
 
 #ifdef __HEI_ENABLE_HW_WRITE
 
-bool registerWrite(const Chip& i_chip, void* i_buffer, size_t& io_bufSize,
-                   uint64_t i_regType, uint64_t i_address)
+bool registerWrite(const Chip& i_chip, RegisterType_t i_regType,
+                   uint64_t i_address, uint64_t i_value)
 {
     bool accessFailure = false;
 
-    HEI_ASSERT(nullptr != i_buffer);
-    HEI_ASSERT(0 != io_bufSize);
-
     switch (i_regType)
     {
         // TODO: add cases for REG_TYPE_SCOM and REG_TYPE_ID_SCOM
         default:
             accessFailure = true;
-            HEI_ERR("registerWrite(%p,%p,%" PRIu64 ",%" PRIx64 ",%" PRIx64 ")",
-                    i_chip.getChip(), i_buffer, (uint64_t)io_bufSize, i_regType,
-                    i_address);
+            HEI_ERR("registerWrite(%p,%" PRIu8 ",%" PRIx64 ",%" PRIx64 ")",
+                    i_chip.getChip(), i_regType, i_address, i_value);
     }
 
     return accessFailure;