CHAPTER 3
3.4.5 USB Port Circuitry (Optional)
Figure 3-7 shows the USB circuitry. This circuitry resides on a separate board that attaches to the same connector that the Magnetic Stripe Encoder Connector can use. For configurations that have both the USB Board and a Magnetic Stripe Encoder, this board supplies a connector (J1) that carries through the connector signals. J1 resides just above the non-USB connection point.
The USB Chip (U2) includes hard wired programming that deals with the USB Protocols. Additionally, the chip has four FIFOs, or Endpoint Registers. One register is initialized with data characterizing the requirements of the Card Printer. The Host accesses this register to supply Address Data. A FIFO is designated as a Data Register.
The CPU Board accesses the Board through the CS SUP, R_W/, and A0 lines. Data between devices travels over the D+ and D- lines. When the FIFO designated for data reception reaches full status, U2 activates the IRQ4 line, an Interrupt Input to the Micro Controller. Note that the D+ and D- line are not differential. USB devices support
J1
USB BOARD
J2 |
| CS_SUP |
| U2 |
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1 |
| /CS |
| Magnetic |
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. |
| R_W/ |
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D16~D31 | /RD |
| Stripe |
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IRQ4 | /WR |
| Encoder |
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| INT |
| Connection |
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18 | R_W/ |
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10k | DRQ |
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19 | CS_MAG | Vcc | /DACK |
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20 |
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| J3 | |||
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21 | RESET/ | A0 |
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| 0.35 | 1 |
OUTPUT | A0 |
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22 | EXT2 |
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| D – |
| 2 |
23 | REFERENCE |
| D0 | D+ | 0.35 | 3 |
24 | IRQ4 |
| D1 |
| 22pF 22pF | 4 |
25 | E ENCOD |
| D2 |
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26 | A1 | D24~D31 | D3 |
| 1.3k |
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27 | A0 | D4 |
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28 | CS_SUP |
| D5 |
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29 | EXT3 |
| D6 |
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30 | GND |
| D7 |
| 10nF 10nF |
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31 | Vdd | RESET/ |
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32 | GND | /RST | 3.3V |
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33 | Vdd |
| MODE0 | AGND |
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34 |
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| MODE1 |
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| U3 | CLKOUT |
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| CLK | XIN |
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| 24MHz |
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| Clock | XOUT |
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CPU Board
Micro Controller
Signals
