diff --git a/Makefile b/Makefile
index 98594a9..b3fc9ca 100644
--- a/Makefile
+++ b/Makefile
@@ -3,22 +3,36 @@
 src = basic.asm
 
 .PHONY: all
-all: basic.img basic.com
+all: basic.img basic.com basic.rom
+
+basic.rom: $(src) addchecksum
+	nasm -f bin -o $@.tmp -Dbootrom $(src)
+	dd if=/dev/zero of=$@ bs=1 count=1024
+	dd if=$@.tmp of=$@ bs=1 conv=notrunc
+	./addchecksum $@ || rm $@
+	rm $@.tmp
 
 basic.img: $(src)
-	nasm -f bin -o $@ $(src)
+	nasm -f bin -o $@ -Dbootsect $(src)
 
 basic.com: $(src)
-	nasm -f bin -o $@ -Dcom_file=1 $(src)
+	nasm -f bin -o $@ -Dcom_file $(src)
+
+addchecksum: addchecksum.c
+	gcc -o $@ $< -Wall
 
 .PHONY: clean
 clean:
-	$(RM) basic.img basic.com
+	$(RM) basic.img basic.com basic.rom addchecksum
 
 .PHONY: rundosbox
 rundosbox: basic.com
 	dosbox $<
 
-.PHONY: runqemu
-runqemu: basic.img
+.PHONY: runqemufd
+runqemufd: basic.img
 	qemu-system-i386 -fda basic.img
+
+.PHONY: runqemurom
+runqemurom: basic.rom
+	qemu-system-i386  -net none -option-rom basic.rom
diff --git a/README b/README
index 064ceaf..45c7bad 100644
--- a/README
+++ b/README
@@ -5,7 +5,7 @@
 | |_) | (_) | (_) | |_| |_/ / | | |/\__/ /_| |_| \__/\
 |_.__/ \___/ \___/ \__\____/\_| |_/\____/ \___/ \____/
 
-bootBASIC interpreter in 512 bytes (boot sector or COM file)
+bootBASIC interpreter in 512 bytes (boot sector, ROM BIOS or COM file)
 by Oscar Toledo G. Jul/22/2019
 
 http://nanochess.org
@@ -20,14 +20,29 @@ If you want to assemble it, you must download the Netwide Assembler
 
 Use this command line:
 
-  nasm -f bin basic.asm -Dcom_file=1 -o basic.com
-  nasm -f bin basic.asm -Dcom_file=0 -o basic.img
+  nasm -f bin basic.asm -Dcom_file -o basic.com
+  nasm -f bin basic.asm -Dbootsect -o basic.img
+
+To create a ROM image, you need to calculate the checksum. To do this,
+there is a program addchecksum. It can be compiled with the gcc
+compiler. As a result, the assembly of the ROM image will look
+like this:
+
+  gcc addchecksum.c -o addchecksum
+  nasm -f bin basic.asm -Dbootrom -o basic.rom
+  ./addchecksum basic.rom || rm basic.rom
 
 Tested with VirtualBox for Mac OS X running Windows XP running this
 interpreter, it also works with DosBox and probably with qemu:
 
   qemu-system-x86_64 -fda basic.img
 
+or
+
+  qemu-system-i386  -net none -option-rom basic.rom
+
+for ROM BIOS.
+
 Enjoy it!
 
 
diff --git a/addchecksum b/addchecksum
new file mode 100755
index 0000000..0b9c29e
Binary files /dev/null and b/addchecksum differ
diff --git a/addchecksum.c b/addchecksum.c
new file mode 100644
index 0000000..a49703d
--- /dev/null
+++ b/addchecksum.c
@@ -0,0 +1,29 @@
+/* addchecksum.c -- Calculate byte-wise checksum and overwrite last byte for PCI 
+ * Copyright (C) 2014, Tobias Kaiser <mail@tb-kaiser.de>
+ */ 
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[]) {
+    if(argc!=2) {
+        fprintf(stderr, "Usage: %s FILE\n\n", argv[0]);
+        exit(1);
+    }
+    FILE *f=fopen(argv[1], "r+");
+    if(!f) {
+        perror("fopen failed");
+        exit(1);
+    }
+    fseek(f, 0, SEEK_END);
+    int f_size=ftell(f);
+    fseek(f, 0, SEEK_SET);
+    unsigned char sum=0;
+    int i;
+    for(i=0;i<f_size-1;i++) {
+        sum+=fgetc(f);
+    }
+    fputc((0x100-sum)&0xff, f);
+    fclose(f);
+    return 0; 
+}
diff --git a/basic.asm b/basic.asm
index 815df6d..9e4ca06 100644
--- a/basic.asm
+++ b/basic.asm
@@ -138,16 +138,21 @@
 
         cpu 8086
 
-    %ifndef com_file    ; If not defined create a boot sector
-com_file:       equ 0
-    %endif
-
-    %if com_file
+    %ifdef com_file
         org 0x0100
-    %else
+    %endif
+    %ifdef bootsect
         org 0x7c00
     %endif
-
+    %ifdef bootrom
+        org 0
+        rom_size_multiple_of equ 512
+        bits 16
+        ; PCI Expansion Rom Header
+        ; ------------------------
+        db 0x55, 0xAA ; signature
+        db rom_size/512; initialization size in 512 byte blocks
+    %endif
 vars:       equ 0x7e00  ; Variables (multiple of 256)
 line:       equ 0x7e80  ; Line input
 
@@ -160,8 +165,7 @@ max_length: equ 20      ; Maximum length of line
 max_size:   equ max_line*max_length ; Max. program size
 
 start:
-    %if com_file
-    %else
+    %ifndef com_file
         push cs         ; For boot sector
         push cs         ; it needs to setup
         push cs         ; DS, ES and SS.
@@ -591,9 +595,13 @@ statements:
         ;
         ; Boot sector filler
         ;
-    %if com_file
-    %else
+    %ifdef bootsect
         times 510-($-$$) db 0x4f
         db 0x55,0xaa            ; Make it a bootable sector
     %endif
-
+    %ifdef bootrom
+        db 0 ; reserve at least one byte for checksum
+        rom_end equ $-$$
+        rom_size equ (((rom_end-1)/rom_size_multiple_of)+1)*rom_size_multiple_of
+;       times rom_size - rom_end db 0 ; padding
+    %endif
diff --git a/basic.com b/basic.com
index 1abd836..a62e4a3 100644
Binary files a/basic.com and b/basic.com differ
diff --git a/basic.img b/basic.img
index b94a0cc..3157ae4 100644
Binary files a/basic.img and b/basic.img differ
diff --git a/basic.rom b/basic.rom
new file mode 100644
index 0000000..4cfafc0
Binary files /dev/null and b/basic.rom differ