diff --git a/src/greaseweazle/codec/codec.py b/src/greaseweazle/codec/codec.py
index 10a3dfe..790bafa 100644
--- a/src/greaseweazle/codec/codec.py
+++ b/src/greaseweazle/codec/codec.py
@@ -159,6 +159,7 @@ def __init__(self, name: Optional[str],
 from greaseweazle.codec.hp import hp_mmfm
 from greaseweazle.codec.northstar import northstar
 from greaseweazle.codec.micropolis import micropolis
+from greaseweazle.codec.datageneral import datageneral
 
 def mk_trackdef(format_name: str) -> TrackDef:
     if format_name in ['amiga.amigados']:
@@ -181,6 +182,8 @@ def mk_trackdef(format_name: str) -> TrackDef:
         return apple2_gcr.Apple2GCRDef(format_name)
     if format_name in ['bitcell']:
         return bitcell.BitcellTrackDef(format_name)
+    if format_name in ['datageneral']:
+        return datageneral.DataGeneralDef(format_name)
     raise error.Fatal('unrecognised format name: %s' % format_name)
 
 
diff --git a/src/greaseweazle/codec/datageneral/__init__.py b/src/greaseweazle/codec/datageneral/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/greaseweazle/codec/datageneral/datageneral.py b/src/greaseweazle/codec/datageneral/datageneral.py
new file mode 100644
index 0000000..cac26c3
--- /dev/null
+++ b/src/greaseweazle/codec/datageneral/datageneral.py
@@ -0,0 +1,247 @@
+# greaseweazle/codec/datageneral.py
+#
+# Written & released by Keir Fraser <keir.xen@gmail.com>
+#
+# This is free and unencumbered software released into the public domain.
+
+from typing import List, Optional
+
+import struct
+from bitarray import bitarray
+import crcmod.predefined
+import itertools as it
+from enum import Enum
+
+from greaseweazle import error
+from greaseweazle.codec import codec
+from greaseweazle.codec.ibm.ibm import decode, encode, fm_encode, mfm_encode
+from greaseweazle.track import MasterTrack, PLL, PLLTrack
+from greaseweazle.flux import HasFlux
+
+default_revs = 1
+
+bad_sector = b'-=[BAD SECTOR]=-'
+
+mfm_sync = bitarray(endian='big')
+mfm_sync.frombytes(mfm_encode(encode(b'\x00\xfb')))
+
+fm_sync = bitarray(endian='big')
+fm_sync.frombytes(fm_encode(encode(b'\x00\x00\x00\x00\x00\x01')))
+
+
+#Sector starts with 23 * 16 zero bits, then a 0001 sync word followed by the adress field
+#There is an 18us "splice" between the address field and the following data field sync 
+#The documentation is not very clear on the exact number of bits in the data sync field
+#The splice plus the data sync add up to a non-integer number of bits, so we 
+#need to search for the data sync pattern to locate the data
+
+#"Manual" FM encoding....
+fm_datasync = bitarray("101010101010101010101010101010101010101010101010101010101011")
+
+
+def csum(dat):
+    #CRC with poly x^16 + x^8 + 1
+    
+    y = 0
+    #Need to "clock in" 8 extra bits to get the correct result    
+    for x in dat + b'\x00':
+        y = ((y & 0xFF) ^ (y >> 8)) |  (((y & 0xFF) ^ x) << 8)
+    return y
+
+class Mode(Enum):
+    FM, MFM = range(2)
+    def __str__(self):
+        NAMES = [ 'Data General FM', 'Data General MFM' ]
+        return f'{NAMES[self.value]}'
+
+class DataGeneral(codec.Codec):
+
+    time_per_rev = 0.166
+
+    verify_revs: float = default_revs
+
+    def __init__(self, cyl: int, head: int, config):
+        if config.mode is Mode.FM:
+            self.clock = 2e-6
+            self.bps = 512
+            self.sync = fm_sync
+            self.datasync = fm_datasync
+            self.presync_bytes = 21
+            self.sync_bytes = 6
+        else:
+            self.clock = 2e-6
+            self.bps = 512
+            self.sync = mfm_sync
+            self.presync_bytes = 34
+            self.sync_bytes = 2
+        self.cyl, self.head = cyl, head
+        self.config = config
+        self.sector: List[Optional[bytes]]
+        self.sector = [None] * self.nsec
+
+    @property
+    def nsec(self) -> int:
+        return self.config.secs
+
+    def summary_string(self) -> str:
+        nsec, nbad = self.nsec, self.nr_missing()
+        s = "%s (%d/%d sectors)" % (self.config.mode, nsec - nbad, nsec)
+        return s
+
+    # private
+    def add(self, sec_id, data) -> None:
+        assert not self.has_sec(sec_id)
+        self.sector[sec_id] = data
+
+    def has_sec(self, sec_id: int) -> bool:
+        return self.sector[sec_id] is not None
+
+    def nr_missing(self) -> int:
+        return len([sec for sec in self.sector if sec is None])
+
+    def get_img_track(self) -> bytearray:
+        tdat = bytearray()
+        for sec in self.sector:
+            tdat += sec if sec is not None else bad_sector * (self.bps//16)
+        return tdat
+
+    def set_img_track(self, tdat: bytes) -> int:
+        totsize = self.nsec * self.bps
+        if len(tdat) < totsize:
+            tdat += bytes(totsize - len(tdat))
+        for sec in range(self.nsec):
+            self.sector[sec] = tdat[sec*self.bps:(sec+1)*self.bps]
+        return totsize
+
+    def decode_flux(self, track: HasFlux, pll: Optional[PLL]=None) -> None:
+        flux = track.flux()
+        if flux.time_per_rev < self.time_per_rev / 2:
+            flux.identify_hard_sectors()
+        flux.cue_at_index()
+        raw = PLLTrack(time_per_rev = self.time_per_rev,
+                       clock = self.clock, data = flux, pll = pll)
+
+        for rev in range(len(raw.revolutions)):
+
+            if self.nr_missing() == 0:
+                break
+
+            bits, _ = raw.get_revolution(rev)
+
+            hardsector_bits = raw.revolutions[rev].hardsector_bits
+            if hardsector_bits is not None:
+                hardsector_bits = list(it.accumulate(hardsector_bits))
+            else:
+                hardsector_bits = [len(bits)*(i+1)//self.nsec
+                                   for i in range(self.nsec)]
+            error.check(len(hardsector_bits) == self.nsec,
+                        f'Data General: Unexpected number of sectors: '
+                        f'{len(hardsector_bits)}')
+            hardsector_bits = [0] + hardsector_bits
+
+            for sec_id in range(self.nsec):
+
+                if self.has_sec(sec_id):
+                    continue
+
+                s, e = hardsector_bits[sec_id], hardsector_bits[sec_id+1]
+                #print(bits[s:e])
+                data = decode(bits[s:e].tobytes())
+                #print(data.hex())
+                offs = bits[s:e].search(self.sync)
+                if (off := next(offs, None)) is None:
+                    continue
+                off += (self.sync_bytes) * 16
+                data = decode(bits[s+off:s+off+2*16].tobytes())
+                #print(data.hex())
+                track = data[0] & 0x7F
+                sector = data[1] >> 2
+                #print(f'Track {track}, Sector {sector}')
+
+                
+                dataoffs = bits[s+off+2*16:e].search(self.datasync)
+                
+                if (dataoff := next(dataoffs, None)) is None:
+                    continue
+
+                data = decode(bits[s+off+2*16 + dataoff + len(self.datasync) :s+off+2*16 + dataoff + len(self.datasync) + 518*16].tobytes())
+                #print(data[:512].hex())
+                #print(data[512:514].hex())
+                #print(data[514:].hex())
+                #print(hex(csum(data[:512])))
+                if  csum(data[:512])== int.from_bytes(data[512:514], 'big'):
+                    self.add(sec_id, data[:512])
+                else:
+                    pass
+                
+
+
+    def master_track(self) -> MasterTrack:
+        raise error.Fatal('NOT IMPLEMENTED')
+        t = bytes()
+        slen = int((self.time_per_rev / self.clock / self.nsec / 16))
+
+        for sec_id in range(self.nsec):
+            s  = encode(bytes(self.presync_bytes))
+            s += encode(b'\xfb' * self.sync_bytes)
+            sector = self.sector[sec_id]
+            data = bad_sector*(self.bps//16) if sector is None else sector
+            s += encode(data + bytes([csum(data)]))
+            s += encode(bytes(slen - len(s)//2))
+            t += s
+
+        t = mfm_encode(t) if self.config.mode is Mode.MFM else fm_encode(t)
+
+        hardsector_bits = [slen*16*i for i in range(self.nsec)]
+
+        track = MasterTrack(bits = t, time_per_rev = self.time_per_rev)
+        track.verify = self
+        return track
+
+
+    def verify_track(self, flux):
+        readback_track = self.__class__(self.cyl, self.head, self.config)
+        readback_track.decode_flux(flux)
+        return (readback_track.nr_missing() == 0
+                and self.sector == readback_track.sector)
+
+
+class DataGeneralDef(codec.TrackDef):
+
+    default_revs = default_revs
+
+    def __init__(self, format_name: str):
+        self.mode: Optional[Mode] = None
+        self.secs: Optional[int] = None
+        self.finalised = False
+
+    def add_param(self, key: str, val) -> None:
+        if key == 'secs':
+            val = int(val)
+            self.secs = val
+        elif key == 'mode':
+            if val == 'fm':
+                self.mode = Mode.FM
+            elif val == 'mfm':
+                self.mode = Mode.MFM
+            else:
+                raise error.Fatal('unrecognised mode %s' % val)
+        else:
+            raise error.Fatal('unrecognised track option %s' % key)
+
+    def finalise(self) -> None:
+        if self.finalised:
+            return
+        error.check(self.secs is not None,
+                    'number of sectors not specified')
+        error.check(self.mode is not None,
+                    'mode not specified')
+        self.finalised = True
+
+    def mk_track(self, cyl: int, head: int) -> DataGeneral:
+        return DataGeneral(cyl, head, self)
+
+
+# Local variables:
+# python-indent: 4
+# End:
diff --git a/src/greaseweazle/data/diskdefs.cfg b/src/greaseweazle/data/diskdefs.cfg
index b8e9a22..13b0ddc 100644
--- a/src/greaseweazle/data/diskdefs.cfg
+++ b/src/greaseweazle/data/diskdefs.cfg
@@ -71,3 +71,4 @@ import sega. "diskdefs_sega.cfg"
 import thomson. "diskdefs_thomson.cfg"
 import tsc. "diskdefs_tsc.cfg"
 import zx. "diskdefs_zx.cfg"
+import datageneral. "diskdefs_datageneral.cfg"
diff --git a/src/greaseweazle/data/diskdefs_datageneral.cfg b/src/greaseweazle/data/diskdefs_datageneral.cfg
new file mode 100644
index 0000000..0829fd5
--- /dev/null
+++ b/src/greaseweazle/data/diskdefs_datageneral.cfg
@@ -0,0 +1,11 @@
+# prefix: datageneral.
+
+disk fm.ss
+     cyls = 77
+     heads = 1
+     tracks * datageneral
+         mode = fm
+         secs = 8
+     end
+end
+