RSDOS (Standard Color Computer Disk Operating system) Reference - Radio Shack TRS-80 Color Computer Disk System Owners Manual & Programming Guide, pages 58-59 sectors 3-11 of the directory track (17) contain Directory Entries, which are 32 bytes made up of:

 byte $00-$07: Filename, left justified, blank-filled.
     If byte 0=0, then file has been deleted.
     If byte 0=$FF, then the entry (and all following entries) have not yet been used.
 byte $08-$0A: Filename extension, left justified, blank-filed
 byte $0b: File type
     0 = BASIC program
     1 = BASIC data file
     2 = Machine-language program
     3 = Text Editor Source file
 byte $0C: ASCII Flag
     0 = the file is in binary format
     $FF = the file is in ASCII format
 byte $0D: The number of the first granule in the file (0-67)
 byte $0E-$0F: The number of bytes in use in the last sector of the file. Big endian.
 byte $16-$1F: Reserved for future use.

sector 2 contains File Allocation Table.