diff --git a/cores/plus_too/readme.md b/cores/plus_too/readme.md
index 55090ad..c69fd5b 100644
--- a/cores/plus_too/readme.md
+++ b/cores/plus_too/readme.md
@@ -30,5 +30,6 @@ Functional changes:
 - various timing simplifications
 - fix mouse counter wrapping
 - Basic sound support
+- SCSI interface + SCSI hdd support
 
 Binaries are available at the [binaries repository](https://github.com/mist-devel/mist-binaries/tree/master/cores/plus_too).
diff --git a/cores/plus_too/scsi.v b/cores/plus_too/scsi.v
index b1261f7..548c38c 100644
--- a/cores/plus_too/scsi.v
+++ b/cores/plus_too/scsi.v
@@ -109,6 +109,7 @@ module scsi(input       sysclk,
 	      cmd_read?buffer_dout:
 	      cmd_inquiry?inquiry_dout:
 	      cmd_read_capacity?read_capacity_dout:
+	      cmd_mode_sense?mode_sense_dout:
 	      8'h00;
    
    // output of inquiry command, identify as "SEAGATE ST225N"
@@ -131,15 +132,24 @@ module scsi(input       sysclk,
 	      8'h00;
 
    // output of read capacity command
-   wire [31:0] capacity = 32'd41055;   // 40960 + 96 blocks = 20MB
+   wire [31:0] capacity = 32'd41056;   // 40960 + 96 blocks = 20MB
+   wire [31:0] capacity_m1 = capacity - 32'd1;
    wire [7:0] read_capacity_dout =
-	      (data_cnt == 32'd0 )?capacity[31:24]:
-	      (data_cnt == 32'd1 )?capacity[23:16]:
-	      (data_cnt == 32'd2 )?capacity[15:8]:
-	      (data_cnt == 32'd3 )?capacity[7:0]:
+	      (data_cnt == 32'd0 )?capacity_m1[31:24]:
+	      (data_cnt == 32'd1 )?capacity_m1[23:16]:
+	      (data_cnt == 32'd2 )?capacity_m1[15:8]:
+	      (data_cnt == 32'd3 )?capacity_m1[7:0]:
 	      (data_cnt == 32'd6 )?8'd2:             // 512 bytes per sector
 	      8'h00;
 
+   wire [7:0] mode_sense_dout =
+	      (data_cnt == 32'd3 )?8'd8:
+	      (data_cnt == 32'd5 )?capacity[23:16]:
+	      (data_cnt == 32'd6 )?capacity[15:8]:
+	      (data_cnt == 32'd7 )?capacity[7:0]:
+	      (data_cnt == 32'd10 )?8'd2:
+	      8'h00;
+
    // clock data out of buffer to allow for embedded ram
    reg [7:0] buffer_dout;
    wire      buffer_out_clk = req && !io_rd;
@@ -278,12 +288,13 @@ module scsi(input       sysclk,
    wire       cmd_inquiry = (op_code == 8'h12);
    wire       cmd_format = (op_code == 8'h04);
    wire       cmd_mode_select = (op_code == 8'h15);
+   wire       cmd_mode_sense = (op_code == 8'h1a);
    wire       cmd_test_unit_ready = (op_code == 8'h00);
    wire       cmd_read_capacity = (op_code == 8'h25);
 
    // valid command in buffer? TODO: check for valid command parameters
    wire       cmd_ok = cmd_read || cmd_write || cmd_inquiry || cmd_test_unit_ready || 
-	        cmd_read_capacity || cmd_mode_select || cmd_format;
+	        cmd_read_capacity || cmd_mode_select || cmd_format || cmd_mode_sense;
      
    // latch parameters once command is complete
    reg [31:0] lba;
@@ -332,7 +343,7 @@ module scsi(input       sysclk,
 						// continue according to command
 
 					        // these commands return data
-					        if(cmd_read || cmd_inquiry || cmd_read_capacity)
+					        if(cmd_read || cmd_inquiry || cmd_read_capacity || cmd_mode_sense)
 						  phase <= `PHASE_DATA_OUT;
 					        // these commands receive dataa
 					        else if(cmd_write || cmd_mode_select)
diff --git a/cores/plus_too/user_io.v b/cores/plus_too/user_io.v
index 3118588..a87138b 100644
--- a/cores/plus_too/user_io.v
+++ b/cores/plus_too/user_io.v
@@ -67,7 +67,7 @@ module user_io #(parameter STRLEN=0) (
 reg [6:0]         sbuf;
 reg [7:0]         cmd;
 reg [2:0] 	      bit_cnt;    // counts bits 0-7 0-7 ...
-reg [7:0]         byte_cnt;   // counts bytes
+reg [9:0]         byte_cnt;   // counts bytes
 reg [5:0]         joystick0;
 reg [5:0]         joystick1;
 reg [3:0] 	      but_sw;
@@ -310,7 +310,7 @@ always@(posedge spi_sck or posedge SPI_SS_IO) begin
 
 	if(SPI_SS_IO == 1) begin
 	   bit_cnt <= 3'd0;
-	   byte_cnt <= 8'd0;
+	   byte_cnt <= 10'd0;
 		sd_ack <= 1'b0;
 		sd_dout_strobe <= 1'b0;
 		sd_din_strobe <= 1'b0;
@@ -322,8 +322,8 @@ always@(posedge spi_sck or posedge SPI_SS_IO) begin
 			sbuf[6:0] <= { sbuf[5:0], SPI_MOSI };
 			
 		bit_cnt <= bit_cnt + 3'd1;
-		if((bit_cnt == 7)&&(byte_cnt != 8'd255)) 
-			byte_cnt <= byte_cnt + 8'd1;
+		if((bit_cnt == 7)&&(byte_cnt != 10'd1023)) 
+			byte_cnt <= byte_cnt + 10'd1;
 
 		// finished reading command byte
       if(bit_cnt == 7) begin
@@ -367,18 +367,16 @@ always@(posedge spi_sck or posedge SPI_SS_IO) begin
 				// send sector IO -> FPGA
 				if(cmd == 8'h17) begin
 					// flag that download begins
-//					sd_dout <= { sbuf, SPI_MOSI};
 					sd_dout_strobe <= 1'b1;
 				end
 				
 				// send sector FPGA -> IO
-				if(cmd == 8'h18)
+				if((cmd == 8'h18) && (byte_cnt < 512))
 					sd_din_strobe <= 1'b1;
 				
 				// send SD config IO -> FPGA
 				if(cmd == 8'h19) begin
 					// flag that download begins
-//					sd_dout <= { sbuf, SPI_MOSI};
 					// sd card knows data is config if sd_dout_strobe is asserted
 					// with sd_ack still being inactive (low)
 					sd_dout_strobe <= 1'b1;