Glen Deas sent me an article about the Ziptape cassette interface, 1978, by the late Lew Edwards. Glen made a PCB for it.

The article about the Fast Cassette Interface is part of my CW Moser Assembler/editor package. Scanned by me in 2010 to the file kimfastcassette.pdf and on my website with the CW Moser package for years now .
Glen Deas knew it was designed by Lew Edwards and entered the source in modern assembler format.


Page 1      A65 65C02 Assembler 1.16
Line#  Loc   Code      Line
1                  
2                  ;-----------------------------------------------------------------------------------------------------------
3                  ;      E:\ZIPTAPE>CSC ZIPTAPE1.ASM
4                  ;
5                   ;     E:\ZIPTAPE>CSC6502 ZIPTAPE1.ASM 
6                   ;           Page 1      File ZIPTAPE1.ASM
7                  ;
8                  ;
9                  ;       ORG $4000
10  4000                    * = $4000
11                  ; ***Irk FAST CASSETTE INTERFACE 
12                  ;    (CONFIGURED FOR KIM)
13                  ;================================================================
14                  ;modified for CSC 6502 Cross Assembler Glen Deas K5GED 1/11/2023
15                  ;================================================================
16                  ;To use this software, enter data in memory locations 0123 
17                  ;as follows:  0123 = LOAD/NO
18                  ;                     0124-0125 = START ADDRESS
19                  ;                     0126-0127 = END ADDRESS
20                  ;The record routine will record from START ADDRESS to END ADDRESS 
21                  ;LOAD/NO has no meaning to the record software.;
22                  ;
23                  ;The load routine will load from START ADDRESS to END ADDRESS 
24                  ;store data in memory onl if LOAD/NO does not =al 0. Where 
25                  ;LOAD/NO can be used for verifying and unconditionally selecting 
26                  ;modules on tape.
27                  ;
28                  ;The load and record routines have callable entry points at 
29                  ;(4000) and CREAD (40A5), and non-ccallable entry points at 
30                  ;LDENTRY (4141) and RCENTRY (4152). If CREAD is called, the
31                  ;Z bit in the PSR will be treu on return if no error was detected
32                  ;and false if errors occurred. If execution is at the non callable
33                  ;entry LDENTRY, a break (via BRK instruction) will be execcuted 
34                  ;at end of loading and register A will indicate if the data was
35                  ;loaded correctly: R(A)=00 for good load, and EE for errors.
36                  ;
37                  ;
38  1702            CPORT = $1702 ;CASSETTE I/O
39  1703            CPORTD = $1703 ;PORT DIRECTION REGISTER 
40                  ;BIT 3 = WRITE TO CASSETTE; BIT 2 - READ FROM CASSETTE
41                  ;
42                  ;
43                  ; :== VARIABLES ==
44  00B2            CHECKSUM           =    $00B2 
45  00B6            ADDRS              =    $00B6 
46  00B6            COUNT              =    ADDRS 
47  00B4            FORMBYTE           =    $00B4 
48  00B4            SYNCCOUNT          =    FORMBYTE
49  00B5            BITCOUNT           =    $00B5
50                  ;
51                  ;INPUT PARMS
52  0123            LOADNO = $0123 
53  0124            TSTART = $0124
54  0126            TEND = $0126
55                  ;
56                  ;CWRITE: WRITE TO TAPE FROM (START) TO (END)
57                  ;
58  4000  AD 03 17  CWRITE LDA CPORTD
59  4003  09 08             ORA #%00001000 ;BIT 3 FOR OUTPUT ON PIA 
60  4005  8D 03 17      STA CPORTD
Page 2      A65 65C02 Assembler 1.16
Line#  Loc   Code      Line
61                  ;THE ABOVE INITIALIZES BIT 3 FOR OUTPUT ON PIA
62  4008  A9 20             LDA #$20 ;32 TIMES 
63  400A  85 B6         STA COUNT
64  400C  A9 16     LPRECST LDA #$16    ;SYNC CHAR.
65  400E  20 41 40      JSR WRITEBYTE
66  4011  A9 10         LDA #$10
67  4013  85 B4         STA SYNCCOUNT
68  4015  20 5D 40  LPDELA JSR OUTZERO
69  4018  C6 B4         DEC SYNCCOUNT
70  401A  D0 F9         BNE LPDELA
71                  ;DELAY TIME FOR SYNC
72  401C  C6 B6         DEC COUNT 
73  401E  D0 EC         BNE LPRECST
74  4020  20 84 40      JSR MOVESTAD
75  4023  A9 0F         LDA #$0F ;RECORD START CHAR. 
76  4025  20 41 40      JSR WRITEBYTE
77  4028  A2 00         LDX #$00
78  402A  86 B2         STX CHECKSUM ;CLEAR CHECKSUM LOW BYTE 
79  402C  86 B3         STX CHECKSUM+1 ;AND HIGH BYTE
80                  ;
81  402E  A1 B6     LOOPDATA LDA (ADDRS,X) ;LOAD DATA INDEXED BY X REG 
82  4030  20 41 40      JSR WRITEBYTE
83  4033  20 8F 40      JSR INCCOMP
84  4036  90 F6         BCC LOOPDATA
85  4038  A5 B3         LDA CHECKSUM+1
86  403A  48            PHA  SAVE HI CKSUM
87  403B  A5 B2         LDA CHECKSUM
88  403D  20 41 40      JSR WRITEBYTE WRITE LO CKSUM FIRST 
89  4040  68            PLA  HI CKSUM NEXT
90                  ;THE ABOVE WRITES BOTH CHECKSUM BYTES
91                  ;
92                  ;ROUTINE TO WRITE A BYTE TO TAPE
93                  ;
94  4041  85 B4     WRITEBYTE STA FORMBYTE
95  4043  20 34 41      JSR CKSUMADD UPDATE CHECKSUM COUNTER
96  4046  20 7C 40      JSR OUTONE START BIT 
97  4049  A9 08         LDA #$08 8 BITS
98  404B  85 B5         STA BITCOUNT
99  404D  06 B4     DATALOOP ASL FORMBYTE SHIFT LEFT INTO CARRY 
100  404F  90 05         BCC ZEROBIT
101  4051  20 7C 40  ONEBIT  JSR OUTONE
102  4054  F0 03         BEQ CKENDBY
103  4056  20 5D 40  ZEROBIT JSR OUTZERO
104  4059  C6 B5     CKENDBY DEC BITCOUNT
105  405B  D0 F0         BNE DATALOOP 
106                  ;NOT OUTPUT 1 STOP BIT
107                  ;
108                  ;ROUTINE OUTPUT A ZERO TO TAPE
109                  ;
110  405D  A9 20     OUTZERO LDA #$20 '0' DELAY CONSTANT 
111                  
112                  ;:ROUTINE WRITE TO TAPE
113                  ;
114  405F  48        WRITE PHA  SAVE DELAY CONSTANT
115  4060  AD 02 17      LDA CPORT
116  4063  09 08         ORA #%00001000 ;OUT A" ON BIT 3
117  4065  8D 02 17      STA CPORT 
118  4068  68            PLA 
119  4069  48            PHA 
120  406A  AA            TAX DELAY CONSTANT
Page 3      A65 65C02 Assembler 1.16
Line#  Loc   Code      Line
121  406B  20 78 40      JSR LOOPD 
122  406E  AD 02 17      LDA CPORT
123  4071  29 F7         AND #%11110111 ;OUT A '01 ON BIT 3 
124  4073  8D 02 17      STA CPORT
125  4076  68            PLA
126  4077  AA            TAX   DELAY CONSTANT
127  4078  CA        LOOPD DEX
128  4079  D0 FD         BNE LOOPD
129  407B  60            RTS
130                  ;
131                  ;ROUTINE OUTPUT A ONE TO TAPE
132                  ;
133  407C  A9 50     OUTONE  LDA #$50 '1' DELAY CONSTANT
134  407E  D0 DF         BNE WRITE
135                  ;DELAY FOR '0' TIME FOR READ 
136                  
137  4080  A2 30     READDELAY LDX #$30
138  4082  D0 F4         BNE LOOPD
139                  ;
140                  ;ROUTINE MOVE FROM START TO ADDRS
141                  ;
142  4084  AD 24 01  MOVESTAD LDA TSTART
143  4087  85 B6         STA ADDRS
144  4089  AD 25 01      LDA TSTART+1
145  408C  85 B7         STA ADDRS+1 
146  408E  60            RTS
147                  ;:ROUTINE INCREMENT AND COMPARE
148                  
149  408F  E6 B6     INCCOMP INC ADDRS
150  4091  D0 02         BNE SKIPINC 
151  4093  E6 B7         INC ADDRS+1
152  4095  A5 B7     SKIPINC    LDA ADDRS+1
153  4097  CD 27 01      CMP TEND+1
154  409A  90 08         BCC NOTEND 
155  409C  A5 B6         LDA ADDRS 
156  409E  CD 26 01      CMP TEND
157  40A1  90 01         BCC NOTEND 
158  40A3  38            SEC
159  40A4  60        NOTEND RTS
160                  ;ON RETURN, C=CLEAR: NOTEND: C=SET: END REACHED
161                  ;
162  40A5  A2 00     CREAD LDX #$00
163  40A7  86 B6         STX COUNT
164  40A9  20 EF 40  LOOPLOAD JSR READBYTE
165  40AC  C9 16         CMP #$16 SYNC
166  40AE  D0 04         BNE SKIP1 
167  40B0  E6 B6         INC COUNT
168  40B2  D0 F5         BNE LOOPLOAD
169  40B4  A4 B6     SKIP1 LDY COUNT
170  40B6  C0 0A         CPY #$0A   ;MUST B >= 10 SYNC'S 
171  40B8  90 EB         BCC CREAD
172  40BA  C9 0F         CMP  #$0F RECORD START
173  40BC  D0 E7         BNE  CREAD
174  40BE  A0 00         LDY #$00
175  40C0  84 B2         STY CHECKSUM
176  40C2  84 B3         STY CHECKSUM+1 LAR CHECKSUM LOCATIONS
177  40C4  20 84 40       JSR MOVESTAD START > ADDRS (2)
178                  ;
179                  ;NOW LOAD DATA
180                  
Page 4      A65 65C02 Assembler 1.16
Line#  Loc   Code      Line
181  40C7  20 EF 40  LOOP69 JSR READBYTE
182  40CA  AC 23 01      LDY LOADNO ;CKG IF TO STORE
183  40CD  F0 02         BEQ SKIPSTOR
184  40CF  81 B6         STA (ADDRS,X)
185  40D1  20 8F 40  SKIPSTOR JSR INCCOMP
186  40D4  90 F1         BCC LOOP69
187  40D6  A5 B3         LDA CHECKSUM+1
188  40D8  48            PHA SAVE CHKSUM HI
189  40D9  A5 B2         LDA CHECKSUM
190  40DB  48            PHA SAVE CHKSUM LO
191  40DC  20 EF 40      JSR READBYTE
192  40DF  68            PLA
193  40E0  C5 B4         CMP FORMBYTE CHECK CHECKSUM LO
194  40E2  D0 07         BNE RETURN
195  40E4  20 EF 40      JSR READBYTE
196  40E7  68            PLA
197  40E8  C5 B4         CMP FORMBYTE CHECK CHECKSUM HI
198  40EA  60            RTS
199  40EB  68        RETURN PLA
200  40EC  A9 FF         LDA #$FF CLEAR Z-BIT
201  40EE  60            RTS
202                  ;ON RETURN Z-BIT = TRUE:GOOD LOAD: Z-BIT ==FALSE: ERROR
203                  ;
204                  ;ROUTINE READ A BYTE FROM TAPE
205                  ;
206  40EF  20 2E 41  READBYTE JSR INPORT
207  40F2  D0 FB         BNE READBYTE LOOP UNTIL 0
208  40F4  20 2E 41  WAITFORI JSR INPORT
209  40F7  F0 FB         BEQ WAITFORI LOOP UNTIL 1
210  40F9  20 80 40      JSR READDELAY
211  40FC  20 2E 41      JSR INPORT
212  40FF  F0 F3         BEQ WAITFORI IF ZERO
213  4101  20 2E 41  WAITFORO JSR INPORT
214  4104  D0 FB         BNE WAITFORO WAIT TIL END OF START BIT
215  4106  A9 08         LDA #$08
216  4108  85 B5         STA BITCOUNT
217  410A  20 2E 41  WAITTOCN JSR INPORT
218  410D  F0 FB         BEQ WAITTOCN ;LOOP UNTIL '1'
219  410F  20 80 40      JSR READDELAY
220  4112  20 2E 41      JSR INPORT
221  4115  F0 08         BEQ PROCESSO IF '0' THENZERO, ELSE ONE
222                  ;
223  4117  20 2E 41  PROCESS1 JSR INPORT
224  411A  D0 FB         BNE PROCESS1 ;LOOP UNTIL '0
225  411C  38            SEC
226  411D  B0 01         BCS ROTATEIN
227  411F  18        PROCESSO CLC
228                  ;
229  4120  26 B4     ROTATEIN ROL FORMBYTE ;ROTATE CARRY
230  4122  C6 B5         DEC BITCOUNT 
231  4124  D0 E4         BNE WAITTOCN 
232  4126  A5 B4         LDA FORMBYTE
233  4128  20 34 41      JSR CKSUMADD UPDATE CHECKSUM
234  412B  A5 B4         LDA FORMBYTE 
235  412D  60            RTS
236                  ;
237                  ;
238                  ;INPUT FROM TAPE
239                  ;
240  412E  AD 02 17  INPORT LDA CPORT
Page 5      A65 65C02 Assembler 1.16
Line#  Loc   Code      Line
241  4131  29 04         AND #%00000100 ;MASK OUT ALL BUT BIT 2 
242  4133  60            RTS
243                  ;
244                  ;
245                  ;UPDATE CHEKSUM COUNTERS
246                  ;
247  4134  18        CKSUMADD CLC
248  4135  D8            CLD
249  4136  65 B2         ADC CHECKSUM+$00 AD R(A) TO CKSUM LO
250  4138  85 B2         STA CHECKSUM+$00
251  413A  A9 00         LDA #$00
252  413C  65 B3         ADC CHECKSUM+1 ADD 00 TO CKSUM HI 
253  413E  85 B3         STA CHECKSUM+1
254  4140  60            RTS
255                  ;
256                  ;
257  4141  20 A5 40  LOADENTRY JSR CREAD
258  4144  D0 08         BNE BAD
259  4146  A9 00         LDA #$00 INDICATE GOOD LOAD BY R(A) =
260  4148  00        B BRK 
261  4149  EA            NOP 
262  414A  EA            NOP
263  414B  4C 41 41      JMP LOADENTRY
264  414E  A9 EE     BAD LDA #$EE  ;INICATE BAD LOAD BY RA)=EE
265  4150  D0 F6         BNE B
266                  ;
267  4152  20 00 40  RECORDENT JSR CWRITE
268  4155  00           BRK
269  4156  EA           NOP 
270  4157  EA           NOP
271  4158  4C 52 41    JMP RECORDENT
272                  
273                  ;END OF PROGRAM
274                  
275  415B             .END
Page 6      A65 65C02 Assembler 1.16
Symbol            Value Line  References
ADDRS             00B6  45    (9) 46 81 143 145 149 151 152 155 184 
BAD               414E  264   (1) 258 
BITCOUNT          00B5  49    (4) 98 104 216 230 
B                 4148  260   (1) 265 
CHECKSUM          00B2  44    (12) 78 79 85 87 175 176 187 189 249 250 252 253 
CKENDBY           4059  104   (1) 102 
CKSUMADD          4134  247   (2) 95 233 
COUNT             00B6  46    (5) 63 72 163 167 169 
CPORT             1702  38    (5) 115 117 122 124 240 
CPORTD            1703  39    (2) 58 60 
CREAD             40A5  162   (3) 257 171 173 
CWRITE            4000  58    (1) 267 
DATALOOP          404D  99    (1) 105 
FORMBYTE          00B4  47    (8) 48 94 99 193 197 229 232 234 
INCCOMP           408F  149   (2) 83 185 
INPORT            412E  240   (7) 206 208 211 213 217 220 223 
LOADENTRY         4141  257   (1) 263 
LOADNO            0123  52    (1) 182 
LOOP69            40C7  181   (1) 186 
LOOPDATA          402E  81    (1) 84 
LOOPD             4078  127   (3) 121 128 138 
LOOPLOAD          40A9  164   (1) 168 
LPDELA            4015  68    (1) 70 
LPRECST           400C  64    (1) 73 
MOVESTAD          4084  142   (2) 74 177 
NOTEND            40A4  159   (2) 154 157 
ONEBIT            4051  101   (0) 
OUTONE            407C  133   (2) 96 101 
OUTZERO           405D  110   (2) 68 103 
PROCESS1          4117  223   (1) 224 
PROCESSO          411F  227   (1) 221 
READBYTE          40EF  206   (5) 164 181 191 195 207 
READDELAY         4080  137   (2) 210 219 
RECORDENT         4152  267   (1) 271 
RETURN            40EB  199   (1) 194 
ROTATEIN          4120  229   (1) 226 
SKIP1             40B4  169   (1) 166 
SKIPINC           4095  152   (1) 150 
SKIPSTOR          40D1  185   (1) 183 
SYNCCOUNT         00B4  48    (2) 67 69 
TEND              0126  54    (2) 153 156 
TSTART            0124  53    (2) 142 144 
WAITFORI          40F4  208   (2) 209 212 
WAITFORO          4101  213   (1) 214 
WAITTOCN          410A  217   (2) 218 231 
WRITEBYTE         4041  94    (4) 65 76 82 88 
WRITE             405F  114   (1) 134 
ZEROBIT           4056  103   (1) 100 
Errors   = 0
Warnings = 0
;184000AD031709088D0317A92085B6A916204140A91085B4205D4007EA
;184018C6B4D0F9C6B6D0EC208440A90F204140A20086B286B3A1B60D92
;184030204140208F4090F6A5B348A5B22041406885B4203441207C0A08
;18404840A90885B506B49005207C40F003205D40C6B5D0F0A920480AF2
;184060AD021709088D02176848AA207840AD021729F78D021768AA0805
;184078CAD0FD60A950D0DFA230D0F4AD240185B6AD250185B760E60E67
;184090B6D002E6B7A5B7CD27019008A5B6CD260190013860A200860B96
;1840A8B620EF40C916D004E6B6D0F5A4B6C00A90EBC90FD0E7A0000EE7
;1840C084B284B320844020EF40AC2301F00281B6208F4090F1A5B30C79
;1840D848A5B24820EF4068C5B4D00720EF4068C5B46068A9FF60200D3E
;1840F02E41D0FB202E41F0FB208040202E41F0F3202E41D0FBA9080C59
;18410885B5202E41F0FB208040202E41F008202E41D0FB38B0011809D7
;18412026B4C6B5D0E4A5B4203441A5B460AD021729046018D865B20B83
;18413885B2A90065B385B36020A540D008A90000EAEA4C4141A9EE0BE0
;0B4150D0F620004000EAEA4C52410575
;00000F000F