1 USB Blaster Cheap Clone
2 =======================
4 The Altera USB Blaster has a cheap clone, based on :
5 - a Cypress CY7C68013A-56PVXC as the main chip
6 - a 74HC244D as the output latch
10 The schematics (cut down to essential) is :
12 /-----------------+----------------------\
13 +--------------+ | | |
14 USB--| CY7C68013A | | +----------+ | |
15 | | | | 74HC244D | | |
17 . . \--o 1 20 o | 10 pins header |
18 | 47 o-- TCK --o 2 19 o---/ +-------+ |
19 | 46 o-- TDO --o 3 18 o-- TCK -----o 1 2 o |
20 | 45 o-- TMS --o 4 17 o-- TDO -----o 3 4 o |
21 | 44 o o 5 16 o-- TMS -----o 5 6 o |
22 | 43 o-- o 6 15 o o 7 8 o |
23 | 42 o-- o 7 14 o +--o 9 10 o |
24 | 41 o-- TDI --o 8 13 o-- ? | +-------+ |
25 . 40 o-- nOE \ o 9 12 o-- TDI --+ |
30 ---------------------------------------/
32 From this one can deduce that :
33 - the cypress emulates the Altera chip
34 - as the cypress pins used are 41-47, all output/input are controlled by 8051
36 - as the 8051 is clocked at 24Mhz, and because each USB byte is handled by the
37 8051, assuming a 40 instruction cycles per USB packet, the maximum throughput
38 would be around 500 kHz.
42 Port A.0: nOE (output enable of 74HC244D)
48 Throughput considerations
49 =========================
50 Mesurements on a scope reveal that :
51 - for bitbang mode, the throughtput is 56.5 kbits/s
52 (as each clock transition is mesured at 17.7us)
53 - for byteshift mode, the throughput is 107.7 kbits/s
54 (as 63 bits TDI transmission is mesured in 585 us)
56 Let's suppose that to upload a 32 bits value, it is necessary to :
57 - move from IDLE to DR-SHIFT : 3 bitbang (3 TMS transitions)
58 - input the 32 bits of data : 1 byteshift (24 bits) + 8 bitbang (8 bits)
59 - move from DR-SHIFT to IDLE : 5 bitbang (5 TMS transitions)
60 So for this 32 bits of data, the time would be :
61 3 * 17.7us + 1 * 585us/63*24 + 5 * 17.7us
62 = 53.1us + 222us + 88.5us
65 Throughtput in bit/s: 32 * (1 / 363E-6) = 88000 bits/s
66 Throughtput in bytes/s: 11kBytes/s
70 Contrary to the original USB Blaster, the cheap clone will never reach high
71 transfer speeds over JTAG.