diff --git a/libraries/mbed/targets/hal/TARGET_Freescale/TARGET_K20D5M/spi_api.c b/libraries/mbed/targets/hal/TARGET_Freescale/TARGET_K20D5M/spi_api.c
index 3075a33a49..2bc6691dfa 100644
--- a/libraries/mbed/targets/hal/TARGET_Freescale/TARGET_K20D5M/spi_api.c
+++ b/libraries/mbed/targets/hal/TARGET_Freescale/TARGET_K20D5M/spi_api.c
@@ -54,7 +54,7 @@ void spi_init(spi_t *obj, PinName mosi, PinName miso, PinName sclk, PinName ssel
     SPIName spi_ssel = (SPIName)pinmap_peripheral(ssel, PinMap_SPI_SSEL);
     SPIName spi_data = (SPIName)pinmap_merge(spi_mosi, spi_miso);
     SPIName spi_cntl = (SPIName)pinmap_merge(spi_sclk, spi_ssel);
-
+    
     obj->spi = (SPI_Type*)pinmap_merge(spi_data, spi_cntl);
     if ((int)obj->spi == NC) {
         error("SPI pinout mapping failed");
@@ -63,9 +63,8 @@ void spi_init(spi_t *obj, PinName mosi, PinName miso, PinName sclk, PinName ssel
     SIM->SCGC5 |= SIM_SCGC5_PORTC_MASK | SIM_SCGC5_PORTD_MASK;
     SIM->SCGC6 |= SIM_SCGC6_SPI0_MASK;
 
-    // halted state
-    obj->spi->MCR &= ~SPI_MCR_MDIS_MASK;
-    obj->spi->MCR |= SPI_MCR_HALT_MASK | SPI_MCR_DIS_RXF_MASK | SPI_MCR_DIS_TXF_MASK;
+    obj->spi->MCR &= ~(SPI_MCR_MDIS_MASK | SPI_MCR_HALT_MASK);
+    //obj->spi->MCR |= SPI_MCR_DIS_RXF_MASK | SPI_MCR_DIS_TXF_MASK;
 
     // set default format and frequency
     if (ssel == NC) {
@@ -77,8 +76,6 @@ void spi_init(spi_t *obj, PinName mosi, PinName miso, PinName sclk, PinName ssel
 
     // not halt in the debug mode
     obj->spi->SR |= SPI_SR_EOQF_MASK;
-    // enable SPI
-    obj->spi->MCR &= (~SPI_MCR_HALT_MASK);
 
     // pin out the spi pins
     pinmap_pinout(mosi, PinMap_SPI_MOSI);
@@ -93,9 +90,9 @@ void spi_free(spi_t *obj) {
     // [TODO]
 }
 void spi_format(spi_t *obj, int bits, int mode, int slave) {
-    if ((bits != 8) && (bits != 16)) {
-        error("Only 8/16 bits SPI supported");
-    }
+    if ((bits < 4) || (bits > 16))
+        error("SPI: Only frames between 4 and 16-bit supported");
+    
 
     if ((mode < 0) || (mode > 3)) {
         error("SPI mode unsupported");
@@ -109,48 +106,45 @@ void spi_format(spi_t *obj, int bits, int mode, int slave) {
     obj->spi->MCR |= ((!slave) << SPI_MCR_MSTR_SHIFT);
 
     // CTAR0 is used
-    obj->spi->CTAR[0] &= ~(SPI_CTAR_CPHA_MASK | SPI_CTAR_CPOL_MASK);
-    obj->spi->CTAR[0] |= (polarity << SPI_CTAR_CPOL_SHIFT) | (phase << SPI_CTAR_CPHA_SHIFT);
+    obj->spi->CTAR[0] &= ~(SPI_CTAR_CPHA_MASK | SPI_CTAR_CPOL_MASK | SPI_CTAR_FMSZ_MASK);
+    obj->spi->CTAR[0] |= (polarity << SPI_CTAR_CPOL_SHIFT) | (phase << SPI_CTAR_CPHA_SHIFT) | ((bits - 1) << SPI_CTAR_FMSZ_SHIFT);
 }
 
 static const uint8_t baudrate_prescaler[] = {2,3,5,7};
-static const uint32_t baudrate_scaler[] = {2, 4, 6, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768};
-static const uint8_t delay_prescaler[] = {1, 3, 5, 7};
+static const uint16_t baudrate_scaler[] = {2,4,6,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768};
 
 void spi_frequency(spi_t *obj, int hz) {
-    uint32_t error = 0;
+    uint32_t f_error = 0;
     uint32_t p_error = 0xffffffff;
     uint32_t ref = 0;
     uint32_t br = 0;
     uint32_t ref_spr = 0;
     uint32_t ref_prescaler = 0;
+    uint32_t ref_dr = 0;
 
     // bus clk
     uint32_t PCLK = bus_frequency();
-    uint32_t divisor = 2;
-    uint32_t prescaler;
 
-    /* TODO */
     for (uint32_t i = 0; i < 4; i++) {
-        prescaler = baudrate_prescaler[i];
-        divisor = 2;
-        for (br = 0; br <= 15; br++, divisor *= 2) {
+        for (br = 0; br <= 15; br++) {
             for (uint32_t dr = 0; dr < 2; dr++) {
-                ref = (PCLK / prescaler) * ((1U + dr) / divisor);
+                ref = (PCLK * (1U + dr) / baudrate_prescaler[i]) / baudrate_scaler[br];
                 if (ref > (uint32_t)hz)
                     continue;
-                error = hz - ref;
-                if (error < p_error) {
+                f_error = hz - ref;
+                if (f_error < p_error) {
                     ref_spr = br;
                     ref_prescaler = i;
-                    p_error = error;
+                    ref_dr = dr;
+                    p_error = f_error;
                 }
             }
         }
     }
 
     // set PBR and BR
-    obj->spi->CTAR[0] = ((ref_prescaler & 0x3) << SPI_CTAR_PBR_SHIFT) | (ref_spr & 0xf);
+    obj->spi->CTAR[0] &= ~(SPI_CTAR_PBR_MASK | SPI_CTAR_BR_MASK | SPI_CTAR_DBR_MASK);
+    obj->spi->CTAR[0] |= (ref_prescaler << SPI_CTAR_PBR_SHIFT) | (ref_spr << SPI_CTAR_BR_SHIFT) | (ref_dr << SPI_CTAR_DBR_SHIFT);
 }
 
 static inline int spi_writeable(spi_t *obj) {
@@ -158,15 +152,15 @@ static inline int spi_writeable(spi_t *obj) {
 }
 
 static inline int spi_readable(spi_t *obj) {
-    return (obj->spi->SR & SPI_SR_RFDF_MASK) ? 0 : 1;
+    return (obj->spi->SR & SPI_SR_RFDF_MASK) ? 1 : 0;
 }
 
 int spi_master_write(spi_t *obj, int value) {
+    //clear RX buffer flag
+    obj->spi->SR |= SPI_SR_RFDF_MASK;
     // wait tx buffer empty
     while(!spi_writeable(obj));
-    obj->spi->PUSHR = SPI_PUSHR_TXDATA(value & 0xff) /*| SPI_PUSHR_EOQ_MASK*/;
-
-    while (!obj->spi->SR & SPI_SR_TCF_MASK); // wait for transfer to be complete
+    obj->spi->PUSHR = SPI_PUSHR_TXDATA(value & 0xffff) /*| SPI_PUSHR_EOQ_MASK*/;
 
     // wait rx buffer full
     while (!spi_readable(obj));