Hi If you look at pg 212 of Oppendahls book, Inside the TRS-80 Model 100, there is a pretty reasonable description of the format.
Quick summary: The bit frequencies are 2400Hz = 1 and 1200Hz = 0. The files consists of two or more blocks, the first block is header with 512 bytes of 55H (or AAH depending on how you start the sync), sync byte 7FH and a file type (9CH = .DO, D0H = .CO and DCH = BA), the file name of six bytes ASCII and 10 further bytes which for .CO files are the start, length and exe addresses. The other blocks start with the same sync pattern and sync byte followed by 8DH then a checksum at the end. DO files are broken into 256byte blocks, the BA and CO files are just one long stream with all the data. The bytes¹ are actually 9bit times so as to allow processing time on the M100, this is a little tricky in how the timing is done as you can find the header and then just see what looks like junk until you then shift the bits back into alignment :) Hope this helps a little. I have a C source file that does a cassette file decode on Teensy 3.6 I can send if that would help? Just let me know directly :) Happy Holidays! From: M100 <[email protected]> on behalf of Charles Hudson <[email protected]> Reply-To: <[email protected]> Date: Tuesday, December 22, 2020 at 8:43 AM To: <[email protected]> Subject: [M100] Cassette file formats > I've been trying to find some information on the format used by the Model 100 > when writing to the CCR-81 (or other tape recorder). I know that there are a > couple of file formats, e.g. text, compressed BASIC, ASCII BASIC and machine > code but I don't know any specifics about any of these formats. > > Practical experiments indicate there are significant differences between what > the M-100 writes and the Model III, but I don't know if they are due to > syntactic or baud-rate or some other differences between the machines. > > Any suggestions for references would be appreciated. > > Thanks, > -CH- > > > <https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.avast. > com%2Fsig-email%3Futm_medium%3Demail%26utm_source%3Dlink%26utm_campaign%3Dsig- > email%26utm_content%3Dwebmail%26utm_term%3Dicon&data=04%7C01%7C%7Cc75c79feed9c > 4b43376708d8a698b897%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637442522148 > 330818%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1 > haWwiLCJXVCI6Mn0%3D%7C1000&sdata=X8MT5axGWhwGiK94WBsjjVwqkkAaa5McNd2xxNSLKeU%3 > D&reserved=0> Virus-free. www.avast.com > <https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.avast. > com%2Fsig-email%3Futm_medium%3Demail%26utm_source%3Dlink%26utm_campaign%3Dsig- > email%26utm_content%3Dwebmail%26utm_term%3Dlink&data=04%7C01%7C%7Cc75c79feed9c > 4b43376708d8a698b897%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637442522148 > 340813%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1 > haWwiLCJXVCI6Mn0%3D%7C1000&sdata=7wUiiu7DRl9uEV2YTq%2Bjsj8fFM8Kt5KdDPisSNiY9QI > %3D&reserved=0> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
