diff --git a/micropython/drivers/storage/sdcard/sdcard.py b/micropython/drivers/storage/sdcard/sdcard.py
index c9c991f59..1c1370c60 100644
--- a/micropython/drivers/storage/sdcard/sdcard.py
+++ b/micropython/drivers/storage/sdcard/sdcard.py
@@ -37,6 +37,20 @@
 _TOKEN_STOP_TRAN = const(0xFD)
 _TOKEN_DATA = const(0xFE)
 
+## This function computes crc7 for SDcard commands
+##   It is not optimized, so do not call it where performance is critical
+##   You should usually be precomputing these values and hardcode them
+#def crc7( cmd:bytes ):
+#    crc = 0
+#    for value in cmd:
+#        for i in range(8):
+#            crc <<= 1
+#            if (value&0x80)^(crc&0x80):
+#                crc ^= 0x09
+#            value <<= 1
+#    return ((crc<<1)|1)&0xFF
+#def cmd_args_to_bytes( cmd:int, args:int ):
+#    return bytes( [cmd|0x40,(args>>24)&0xFF,(args>>16)&0xFF,(args>>8)&0xFF,args&0xFF] )
 
 class SDCard:
     def __init__(self, spi, cs, baudrate=1320000):
@@ -92,7 +106,7 @@ def init_card(self, baudrate):
 
         # get the number of sectors
         # CMD9: response R2 (R1 byte + 16-byte block read)
-        if self.cmd(9, 0, 0, 0, False) != 0:
+        if self.cmd(9, 0, 0xAF, 0, False) != 0:
             raise OSError("no response from SD card")
         csd = bytearray(16)
         self.readinto(csd)
@@ -109,7 +123,7 @@ def init_card(self, baudrate):
         # print('sectors', self.sectors)
 
         # CMD16: set block length to 512 bytes
-        if self.cmd(16, 512, 0) != 0:
+        if self.cmd(16, 512, 0x15) != 0:
             raise OSError("can't set 512 block size")
 
         # set to high data rate now that it's initialised
@@ -118,8 +132,8 @@ def init_card(self, baudrate):
     def init_card_v1(self):
         for i in range(_CMD_TIMEOUT):
             time.sleep_ms(50)
-            self.cmd(55, 0, 0)
-            if self.cmd(41, 0, 0) == 0:
+            self.cmd(55, 0, 0x65)
+            if self.cmd(41, 0, 0xE5) == 0:
                 # SDSC card, uses byte addressing in read/write/erase commands
                 self.cdv = 512
                 # print("[SDCard] v1 card")
@@ -129,10 +143,10 @@ def init_card_v1(self):
     def init_card_v2(self):
         for i in range(_CMD_TIMEOUT):
             time.sleep_ms(50)
-            self.cmd(58, 0, 0, 4)
-            self.cmd(55, 0, 0)
-            if self.cmd(41, 0x40000000, 0) == 0:
-                self.cmd(58, 0, 0, -4)  # 4-byte response, negative means keep the first byte
+            self.cmd(58, 0, 0xFD, 4)
+            self.cmd(55, 0, 0x65)
+            if self.cmd(41, 0x40000000, 0x77) == 0:
+                self.cmd(58, 0, 0xFD, -4)  # 4-byte response, negative means keep the first byte
                 ocr = self.tokenbuf[0]  # get first byte of response, which is OCR
                 if not ocr & 0x40:
                     # SDSC card, uses byte addressing in read/write/erase commands
@@ -250,7 +264,7 @@ def readblocks(self, block_num, buf):
         assert nblocks and not len(buf) % 512, "Buffer length is invalid"
         if nblocks == 1:
             # CMD17: set read address for single block
-            if self.cmd(17, block_num * self.cdv, 0, release=False) != 0:
+            if self.cmd(17, block_num * self.cdv, 0x7F, release=False) != 0:
                 # release the card
                 self.cs(1)
                 raise OSError(5)  # EIO
@@ -258,7 +272,7 @@ def readblocks(self, block_num, buf):
             self.readinto(buf)
         else:
             # CMD18: set read address for multiple blocks
-            if self.cmd(18, block_num * self.cdv, 0, release=False) != 0:
+            if self.cmd(18, block_num * self.cdv, 0x7F, release=False) != 0:
                 # release the card
                 self.cs(1)
                 raise OSError(5)  # EIO
@@ -269,7 +283,7 @@ def readblocks(self, block_num, buf):
                 self.readinto(mv[offset : offset + 512])
                 offset += 512
                 nblocks -= 1
-            if self.cmd(12, 0, 0xFF, skip1=True):
+            if self.cmd(12, 0, 0x61, skip1=True):
                 raise OSError(5)  # EIO
 
     def writeblocks(self, block_num, buf):
@@ -281,14 +295,14 @@ def writeblocks(self, block_num, buf):
         assert nblocks and not err, "Buffer length is invalid"
         if nblocks == 1:
             # CMD24: set write address for single block
-            if self.cmd(24, block_num * self.cdv, 0) != 0:
+            if self.cmd(24, block_num * self.cdv, 0x7F) != 0:
                 raise OSError(5)  # EIO
 
             # send the data
             self.write(_TOKEN_DATA, buf)
         else:
             # CMD25: set write address for first block
-            if self.cmd(25, block_num * self.cdv, 0) != 0:
+            if self.cmd(25, block_num * self.cdv, 0x7F) != 0:
                 raise OSError(5)  # EIO
             # send the data
             offset = 0