Future Technology Devices International Ltd.

Application Note AN_129
Interfacing FTDI USB Hi-Speed
Devices to a JTAG TAP
Document Reference No.: FT000183
Version 1.1
Issue Date: 2011-09-02

This application note describes the use of the FTDI USB Hi-Speed FT232H, FT2232H and FT4232H
devices to emulate a JTAG interface using their MPSSE

Use of FTDI devices in life support and/or safety applications is entirely at the user’s risk, and the user agrees
to defend, indemnify and hold harmless FTDI from any and all damages, claims, suits or expense resulting
from such use.

Future Technology Devices International Limited (FTDI)
Unit 1,2 Seaward Place, Glasgow G41 1HH, United Kingdom
Tel.: +44 (0) 141 429 2777 Fax: + 44 (0) 141 429 2758
E-Mail (Support): support1@ftdichip.com Web: http://www.ftdichip.com

Copyright © 2009 Future Technology Devices International Limited

Document Reference No.: FT000183
Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114

Table of Contents
1

Introduction .................................................................... 2
1.1

FTDI MPSSE Introduction .......................................................... 2

1.2

JTAG background ...................................................................... 2

1.2.1

JTAG signalling.......................................................................................... 4

2

Example Circuit ............................................................... 5

3

Example Program ............................................................ 6
3.1

Code Listing .............................................................................. 6

3.2

Program Output ...................................................................... 11

4

Summary....................................................................... 12

5

Acronyms and Abbreviations ......................................... 13

6

Contact Information ...................................................... 14

Appendix A - References .................................................... 15
Appendix B - List of Figures and Tables ............................. 16
Appendix C - Revision History ............................................ 17

Copyright © 2009-2011 Future Technology Devices International Limited1

Document Reference No.: FT000183
Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114

1

Introduction

The FT2232H and FT4232H are the FTDI’s first USB 2.0 Hi-Speed (480Mbits/s) USB to UART/FIFO ICs.
They also have the capability of being configured in a variety of serial interfaces using the internal MPSSE(Multi-Protocol Synchronous Serial Engine). The FT2232H device has two independent ports, both ofwhich can be configured to use the MPSSE while only Channel A and B of FT4232H can be configured touse the MPSSE.
The FT232H, introduced in 2011, builds on the FTDI Hi-Speed USB family. The FT232H is a single-port
UART/FIFO IC that has one MPSSE interface as well as several new modes.
Using the MPSSE can simplify the synchronous serial protocol (USB to SPI, I2C, JTAG, etc.) design. Thisapplication note focuses on the hardware and software required to emulate a connection to a JTAG TAP
test chain using the FT2232H. Users can use the example schematic and functional software code to
begin their design. Note that software code listing is provided as an illustration only and not supported by
FTDI. The FT232H and FT4232H can also be used with the example in this document, though pin-out
and port selection will need to match the respective part.
The application example also duplicates the JTAG timing expected to be seen by the SN74BCT8244A toprove the function.

1.1 FTDI MPSSE Introduction
The Multi-Protocol Synchronous Serial Engine (MPSSE) is a feature of certain FTDI client ICs that allow
emulation of several synchronous serial protocols including SPI, I2C and JTAG.
A single MPSSE is available in the FT2232D, a Full-Speed USB 2.0 client device. The FT2232D is capableof synchronous serial communication up to 6Mbps.
As noted above, two MPSSEs are available in the FT2232H and the FT4232H, both Hi-Speed USB 2.0
client devices. Each of the engines is capable of synchronous serial communications up to 30Mbps. The
MPSSE in the FT2232H and FT4232H provide new commands for additional clock modes and is used in
CPU interface and synchronous FIFO (parallel) modes. The FT232H contains a single MPSSE, the CPU
Synchronous FIFO and the new FT1248 modes. Application note AN_135, MPSSE Basics and AN_167,
FT1248 Dynamic Parallel/Serial Interface Basics provide more information on these other modes.
This application note describes the use of the MPSSE to emulate a JTAG interface. There are multiplereferences to AN_108 - Command Processor for MPSSE and MCU Host Bus Emulation Modes, alsoavailable from the FTDI Web Site.

1.2 JTAG backgroundToday’s electronic circuits consist of numerous complex integrated circuits. A typical embedded system
can contain multiple CPUs, programmable devices, memory, etc. With such complexity, it is often
impossible to directly probe and test the entire functionality of a given design.
In 1990, the Institute of Electrical and Electronics Engineers (IEEE) ratified the standard 1149.1, which
was the work of the Joint Test Action Group (JTAG). This standard defines a common means of
implementing boundary-scan test functionality in an integrated circuit. It allows devices from different
vendors to be present in a common chain to provide access to all of the Input and Output (I/O) pins.
Commonly used with additional facilities, such as a bed-of-nails device, it is possible to performfunctional and manufacturing tests on an entire circuit. It is common to refer to the IEEE 1149.1
standard as the "JTAG standard". Many published documents and articles use these terms
interchangeably.
The IEEE 1149.1 was most recently updated in 2001. Additional IEEE standards reference 1149.1 whileproviding expanded features such as analog circuit tests in addition to digital circuit tests. These
additional standards are 1149.4 - Analog Boundary Scan, 1149.6 - Advanced I/O and 1532 - In System
Configuration. The latter is commonly used for programming memory devices and configuring
programmable digital logic such as FPGAs and CPLDs.
JTAG (IEEE 1149.1) defines a synchronous state machine consisting of 16 states as noted in Figure 1.1.

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Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114

JTAG TAP State MachineTransitions on state of TMS on positive edge of TCK

1

Test-Logic-Reset
test-logic-reset
0
1

0

1

Run-Test-Idle

1

Select-DR-Scan

Select-IR-Scan

0
1

0
1

Capture-DR

Capture-IR00

Shift-DR

Shift-IR

0

1

0

1
1

Exit1-DR1

Exit1-IR

0

0

Pause-DR

Pause-IR

0

1

0

1

0

0
Exit2-DR

Exit2-IR1

1

Update-DR
update-dr
1Update-IR100Figure 1.1 – IEEE 1149.1 (JTAG) state machine

The boundary scan circuitry is accessed through a Test Access Port (TAP) controller with four dedicatedand mandatory I/O signals: Test Clock (TCK) - the input clock for the state machine, Test Mode Select(TMS) - the input used to navigate through the state machine, Test Data In (TDI) - the input containing
serial data or instructions and Test Data Out (TDO) - the output containing serial data or instructions. An
optional fifth signal, Test Reset (TRST#) can be implemented on a TAP. TRST# is an asynchronous resetthat forces the state machine immediately to the Test-Logic-Reset state. It is important to note thateven without TRST#, the state machine can always be forced to Test-Logic-Reset from any other state byholding TMS high for a maximum of five clock cycles.

TDO
TDI

TDI

TDO

TMS
TCK

TDI

TDO

TMS
TCK

TMS
TCK
Figure 1.2 – IEEE 1149.1 (JTAG) TAP chain

As shown in Figure 1.2, devices in a JTAG chain share TCK and TMS. This forces all devices on a single
chain to be in the same state within the state machine. The JTAG master controller connects its data
output to TDI. Each device in the chain connects its TDI to the previous TDO. Finally, the last device inthe chain connects its TDO to the controllers data input. Other connection schemes are possible;
however, they are beyond the scope of this application note.
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Document Reference No.: FT000183
Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114

1.2.1 JTAG signalling
The IEEE 1149.1 specification identifies state transitions based on the state of TMS at the rising edge ofTCK. Loading of instruction and data stimulus registers within the TAP as well as data shifting into TDI
and out of TDO are also performed on the rising edge of TCK. The falling edge of TCK is used to latch
data responses into the available registers in the boundary scan device. The registers within each JTAGTAP have different widths. It is important to maintain the level of TMS while data is shifted into and/or
out of the registers.
The SN74BCT8244A contains the following JTAG TAP registers:

Register

Size

Instruction

8-bit

Boundary-Scan

18-bitBoundary-Scan Control

2-bit

Bypass

1-bit

Table 1.1 – SN74BCT8244 JTAG TAP registers

If there are multiple devices in a TAP chain each register type can be of a different length for each of thedevices. The JTAG master control program must account for these. There are six states throughout the
JTAG state diagram that are designed to accommodate different devices with different register lengths.
Referring to Figure 1.1, these states are: Test-Logic-Reset, Run-Test-Idle, Shift-DR, Pause-DR, Shift-IR
and Pause-IR. Holding TMS at the appropriate value holds the state machine in the required state until
valid bits are clocked to all registers for all devices in the TAP chain.

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Document Reference No.: FT000183
Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114

2

Example Circuit

A simple integrated circuit with a JTAG TAP is the Texas Instruments SN74BCT8244A (www.ti.com). This
device consists of an octal buffer with two output enable pins and a JTAG TAP to provide the boundary
scan capability. For this example, the FT2232H Mini Module will be used as shown in the circuit excerpt
in Figure 2.1. USB and power connection details can be found in the FT2232H Datasheet, FT2232H MiniModule Datasheet and DLP-USB1232H Datasheet.

18
DI/TDO
17
DO/TDI
19
CS/TMS
16
SK/TCK

14
12
13

Floating Inputs
Pulled HighFT2232H(partial)

SCAN
TDI ‘BCT8244A
11
TMS
TDO
TCK
EN1
EN2
1A1
1A2
1A3
1A4
2A1
2A2
2A3
2A4

1Y1
1Y2
1Y3
1Y4
2Y1
2Y2
2Y3
2Y4

Figure 2.1 – Example circuit

When using the MPSSE, four pins of the FT2232H are defined for the synchronous serial interface. In
addition to the FT2232H itself, two modules that utilize the FT2232H are also listed along with thecorresponding pins.

FT2232H IC Port A

FT2232H Mini Module

DLP-USB1232H

Pin Number

Pin Number

Pin Number

TCK (output)

16

CN2-7

18

TDI (output)

17

CN2-1016

TDO (input)

18

CN2-9

2

TMS (output)

19

CN2-12

5

JTAG Function

Table 2.1 – FT2232H JTAG pin assignments

TDI and TDO appear to be reversed; however, these are the correct signal names as referenced by the
JTAG TAP. The input pins of the SN74BCT8244A are internally pulled high. For this example circuit, they
are left open. This fixes the input values at logic "1" and forces the outputs into a high-impedance state.
For this application note, Port A of the FT2232H is connected to the SN74BCT8244A. With the FT2232H
and FT4232H, Port B could be used instead. In conjunction with the Port B pin assignments, theapplication program (see next section) would also require modification to access the MPSSE for port B.
TRST# is supported on the SN74BCT8244A; however, it requires an input of 10V on the TMS pin. To
simplify the circuit, TRST# is not implemented in this example. Note that on a TAP with a standard I/Ovoltage, one of the unused GPIO pins of the FT2232H could be used for this function.
The FT2232H requires a VCCIO of 3.3V, although its inputs are 5V tolerant. This allows a directconnection with the 5V SN74BCT8244A. Inspection of the two datasheets will show the logic high andlow input thresholds are indeed satisfied as well as maximum voltages not exceeded.

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Document Reference No.: FT000183
Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114

3

Example Program

The timing example on Page 14 of the Texas Instruments SN74BCT8244A datasheet is duplicated and theresultant data observed. This example consists of 25 cycles of TCK. All states of the JTAG TAP controller
are utilized, with the exception of Pause-IR, Exit2-IR, Pause-DR and Exit2-DR. These unused states are
typically only needed when a device has a longer JTAG chain, or very large Boundary-Scan registers.
This example program utilizes the FTDI D2XX device driver. It is written in a linear fashion todemonstrate the actual bytes being sent to the MPSSE and the resultant data read from the MPSSE.
There are sections where reading and writing the data pins (TDI & TDO) must be combined withmanipulating the control pin (TMS) in order to change states. The resultant data must be carefully
observed and acted upon. Data may need shifted into a format that is more useful to the programmer.
In addition to duplicating the timing example, the Hi-Speed FTDI chips (FT2232H and FT4232H) support
generation of TCK without clocking any data into our out of the MPSSE. This is demonstrated toward theend of the program listing. The code listing is followed by scope plots of the expected timing.
NOTE:
The FT2232H and FT4232H require device driver version 2.06.00 or later.
The FT232H requires device driver version 2.08.14 or later.
In general, it is always a good idea to load the latest driver for all FTDI peripheral devices.

3.1 Code Listing
The example program is written in C++ and compiled in Microsoft® Visual Studio 2008 as a console
application.
// AN_129_Hi-Speed_JTAG_with_MPSSE.cpp : Defines the entry point for the console application.
//#include "stdafx.h"#include <windows.h>#include <stdio.h>#include "ftd2xx.h"
int _tmain(int argc, _TCHAR* argv[]){
FT_HANDLE ftHandle;// Handle of the FTDI device
FT_STATUS ftStatus;// Result of each D2XX call
DWORD dwNumDevs;
unsigned int uiDevIndex = 0xF;// The number of devices// The device in the list that is used

BYTE byOutputBuffer[1024];
BYTE byInputBuffer[1024];// Buffer to hold MPSSE commands and data to be sent to the FT2232H// Buffer to hold data read from the FT2232H

DWORD dwCount = 0;
DWORD dwNumBytesToSend = 0;
DWORD dwNumBytesSent = 0;
DWORD dwNumBytesToRead = 0;
DWORD dwNumBytesRead = 0;// General loop index// Index to the output buffer// Count of actual bytes sent - used with FT_Write// Number of bytes available to read in the driver's input buffer// Count of actual bytes read - used with FT_Read

DWORD dwClockDivisor = 0x05DB;// Value of clock divisor, SCL Frequency = 60/((1+0x05DB)*2) (MHz) = 20khz// Does an FTDI device exist?
printf("Checking for FTDI devices...\n");ftStatus = FT_CreateDeviceInfoList(&dwNumDevs);// Get the number of FTDI devices
if (ftStatus != FT_OK)// Did the command execute OK?
{
printf("Error in getting the number of devices\n");return 1;// Exit with error}
if (dwNumDevs < 1)// Exit if we don't see any{
printf("There are no FTDI devices installed\n");return 1;// Exist with error}
printf("%d FTDI devices found - the count includes individual ports on a single chip\n", dwNumDevs);

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Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114// Open the port - For this application note, assume the first device is a FT2232H or FT4232H// Further checks can be made against the device descriptions, locations, serial numbers, etc.
//
before opening the port.
printf("\nAssume first device has the MPSSE and open it...\n");ftStatus = FT_Open(0, &ftHandle);
if (ftStatus != FT_OK){
printf("Open Failed with error %d\n", ftStatus);
return 1;// Exit with error}// Configure port parameters
printf("\nConfiguring port for MPSSE use...\n");ftStatus |= FT_ResetDevice(ftHandle);//Reset USB device//Purge USB receive buffer first by reading out all old data from FT2232H receive buffer
ftStatus |= FT_GetQueueStatus(ftHandle, &dwNumBytesToRead);// Get the number of bytes in the FT2232H receive bufferif ((ftStatus == FT_OK) && (dwNumBytesToRead > 0))
FT_Read(ftHandle, &byInputBuffer, dwNumBytesToRead, &dwNumBytesRead);//Read out the data from FT2232H receive buffer
ftStatus |= FT_SetUSBParameters(ftHandle, 65536, 65535);//Set USB request transfer sizes to 64K
ftStatus |= FT_SetChars(ftHandle, false, 0, false, 0);//Disable event and error characters
ftStatus |= FT_SetTimeouts(ftHandle, 0, 5000);//Sets the read and write timeouts in milliseconds
ftStatus |= FT_SetLatencyTimer(ftHandle, 16);//Set the latency timer (default is 16mS)
ftStatus |= FT_SetBitMode(ftHandle, 0x0, 0x00);//Reset controller
ftStatus |= FT_SetBitMode(ftHandle, 0x0, 0x02);//Enable MPSSE mode
if (ftStatus != FT_OK){
printf("Error in initializing the MPSSE %d\n", ftStatus);
FT_Close(ftHandle);
return 1;// Exit with error}
Sleep(50); // Wait for all the USB stuff to complete and work// ----------------------------------------------------------// At this point, the MPSSE is ready for commands// ----------------------------------------------------------// ----------------------------------------------------------// Synchronize the MPSSE by sending a bogus opcode (0xAA),//
The MPSSE will respond with "Bad Command" (0xFA) followed by//
the bogus opcode itself.
// ----------------------------------------------------------byOutputBuffer[dwNumBytesToSend++] = 0xAA;//'\xAA';//Add bogus command ‘xAA’ to the queue
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the BAD commands
dwNumBytesToSend = 0;// Reset output buffer pointerdo{ftStatus = FT_GetQueueStatus(ftHandle, &dwNumBytesToRead);// Get the number of bytes in the device input buffer} while ((dwNumBytesToRead == 0) && (ftStatus == FT_OK));//or Timeoutbool bCommandEchod = false;
ftStatus = FT_Read(ftHandle, &byInputBuffer, dwNumBytesToRead, &dwNumBytesRead);//Read out the data from input bufferfor (dwCount = 0; dwCount < dwNumBytesRead - 1; dwCount++)//Check if Bad command and echo command received{if ((byInputBuffer[dwCount] == 0xFA) && (byInputBuffer[dwCount+1] == 0xAA)){
bCommandEchod = true;break;}}
if (bCommandEchod == false){
printf("Error in synchronizing the MPSSE\n");FT_Close(ftHandle);
return 1;// Exit with error}// ----------------------------------------------------------// Configure the MPSSE settings for JTAG//
Multple commands can be sent to the MPSSE with one FT_Write// ----------------------------------------------------------dwNumBytesToSend = 0;// Start with a fresh index// Set up the Hi-Speed specific commands for the FTx232H
byOutputBuffer[dwNumBytesToSend++] = 0x8A;// Use 60MHz master clock (disable divide by 5)
byOutputBuffer[dwNumBytesToSend++] = 0x97;// Turn off adaptive clocking (may be needed for ARM)
byOutputBuffer[dwNumBytesToSend++] = 0x8D;// Disable three-phase clocking
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the HS-specific commands

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Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114
dwNumBytesToSend = 0;// Reset output buffer pointer// Set initial states of the MPSSE interface - low byte, both pin directions and output values//
Pin name
Signal Direction
Config Initial State
Config//
ADBUS0TCK
output1
low
0//
ADBUS1TDI
output1
low
0//
ADBUS2
TDO
input
0
0
//
ADBUS3TMS
output1high
1//
ADBUS4GPIOL0 input
00//
ADBUS5GPIOL1 input
00//
ADBUS6GPIOL2 input
00//
ADBUS7GPIOL3 input
00
byOutputBuffer[dwNumBytesToSend++] = 0x80;// Set data bits low-byte of MPSSE port
byOutputBuffer[dwNumBytesToSend++] = 0x08;// Initial state config above
byOutputBuffer[dwNumBytesToSend++] = 0x0B;// Direction config above
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the low GPIO config commands
dwNumBytesToSend = 0;// Reset output buffer pointer// Set initial states of the MPSSE interface - high byte, both pin directions and output values//
Pin name
Signal Direction
Config Initial State
Config//
ACBUS0GPIOH0 input
00//
ACBUS1
GPIOH1 input
00//
ACBUS2
GPIOH2 input
00//
ACBUS3
GPIOH3 input
00//
ACBUS4
GPIOH4 input
00//
ACBUS5GPIOH5 input
00//
ACBUS6
GPIOH6 input
00//
ACBUS7
GPIOH7 input
00
byOutputBuffer[dwNumBytesToSend++] = 0x82;// Set data bits low-byte of MPSSE port
byOutputBuffer[dwNumBytesToSend++] = 0x00;// Initial state config above
byOutputBuffer[dwNumBytesToSend++] = 0x00;// Direction config above
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the high GPIO config commands
dwNumBytesToSend = 0;// Reset output buffer pointer// Set TCK frequency// TCK = 60MHz /((1 + [(1 +0xValueH*256) OR 0xValueL])*2)
byOutputBuffer[dwNumBytesToSend++] = '\x86';//Command to set clock divisor
byOutputBuffer[dwNumBytesToSend++] = dwClockDivisor & 0xFF;//Set 0xValueL of clock divisor
byOutputBuffer[dwNumBytesToSend++] = (dwClockDivisor >> 8) & 0xFF;//Set 0xValueH of clock divisor
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the clock divisor commands
dwNumBytesToSend = 0;// Reset output buffer pointer// Disable internal loop-backbyOutputBuffer[dwNumBytesToSend++] = 0x85;// Disable loopback
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the loopback command
dwNumBytesToSend = 0;// Reset output buffer pointer// Navigage TMS through Test-Logic-Reset -> Run-Test-Idle -> Select-DR-Scan -> Select-IR-Scan
//
TMS=1
TMS=0
TMS=1
TMS=1
byOutputBuffer[dwNumBytesToSend++] = 0x4B;// Don't read data in Test-Logic-Reset, Run-Test-Idle, Select-DR-Scan, Select-IR-Scan
byOutputBuffer[dwNumBytesToSend++] = 0x05;// Number of clock pulses = Length + 1 (6 clocks here)
byOutputBuffer[dwNumBytesToSend++] = 0x0D;// Data is shifted LSB first, so the TMS pattern is 101100
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the TMS command
dwNumBytesToSend = 0;// Reset output buffer pointer// TMS is currently low.
// State machine is in Shift-IR, so now use the TDI/TDO command to shift 1's out TDI/DO while reading TDO/DI// Although 8 bits need shifted in, only 7 are clocked here. The 8th will be in conjunciton with a TMS command, coming next
byOutputBuffer[dwNumBytesToSend++] = 0x3B;// Clock data out throuth states Capture-IR, Shift-IR and Exit-IR, read back result
byOutputBuffer[dwNumBytesToSend++] = 0x06;// Number of clock pulses = Length + 1 (7 clocks here)
byOutputBuffer[dwNumBytesToSend++] = 0xFF;// Shift out 1111111 (ignore last bit)
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the TMS command
dwNumBytesToSend = 0;// Reset output buffer pointerCopyright © 2009-2011 Future Technology Devices International Limited

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Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114// Here is the TMS command for one clock.

Data is also shifted in.

byOutputBuffer[dwNumBytesToSend++] = 0x6B;// Clock out TMS, Read one bit.
byOutputBuffer[dwNumBytesToSend++] = 0x00;// Number of clock pulses = Length + 0 (1 clock here)
byOutputBuffer[dwNumBytesToSend++] = 0x83;// Data is shifted LSB first, so TMS becomes 1. Also, bit 7 is shifted into TDI/DO, also a 1// The 1 in bit 1 will leave TMS high for the next commands.
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the TMS command
dwNumBytesToSend = 0;// Reset output buffer pointer// Navigage TMS from Exit-IR through Update-IR -> Select-DR-Scan -> Capture-DR
//
TMS=1
TMS=1
TMS=0
byOutputBuffer[dwNumBytesToSend++] = 0x4B;// Don't read data in Update-IR -> Select-DR-Scan -> Capture-DR
byOutputBuffer[dwNumBytesToSend++] = 0x03;// Number of clock pulses = Length + 1 (4 clocks here)
byOutputBuffer[dwNumBytesToSend++] = 0x83;// Data is shifted LSB first, so the TMS pattern is 110
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the TMS command
dwNumBytesToSend = 0;// Reset output buffer pointer// TMS is currently low.
// State machine is in Shift-DR, so now use the TDI/TDO command to shift 101 out TDI/DO while reading TDO/DI// Although 3 bits need shifted in, only 2 are clocked here. The 3rd will be in conjunciton with a TMS command, coming next
byOutputBuffer[dwNumBytesToSend++] = 0x3B;// Clock data out throuth states Shift-DR and Exit-DR.
byOutputBuffer[dwNumBytesToSend++] = 0x01;// Number of clock pulses = Length + 1 (2 clocks here)
byOutputBuffer[dwNumBytesToSend++] = 0x01;// Shift out 101 (ignore last bit)
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the TMS command
dwNumBytesToSend = 0;// Reset output buffer pointer// Here is the TMS command for one clock.

Data is also shifted in.

byOutputBuffer[dwNumBytesToSend++] = 0x6B;// Clock out TMS, Read one bit.
byOutputBuffer[dwNumBytesToSend++] = 0x00;// Number of clock pulses = Length + 0 (1 clock here)
byOutputBuffer[dwNumBytesToSend++] = 0x83;// Data is shifted LSB first, so TMS becomes 1. Also, bit 7 is shifted into TDI/DO, also a 1// The 1 in bit 1 will leave TMS high for the next commands.
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the TMS command
dwNumBytesToSend = 0;// Reset output buffer pointer// Navigage TMS through Update-DR -> Select-DR-Scan -> Select-IR-Scan -> Test Logic Reset
//
TMS=1
TMS=1
TMS=1
TMS=1
byOutputBuffer[dwNumBytesToSend++] = 0x4B;// Don't read data in Update-DR -> Select-DR-Scan -> Select-IR-Scan -> Test Logic Reset
byOutputBuffer[dwNumBytesToSend++] = 0x03;// Number of clock pulses = Length + 1 (4 clocks here)
byOutputBuffer[dwNumBytesToSend++] = 0xFF;// Data is shifted LSB first, so the TMS pattern is 101100
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the TMS command
dwNumBytesToSend = 0;// Reset output buffer pointerdo{ftStatus = FT_GetQueueStatus(ftHandle, &dwNumBytesToRead);// Get the number of bytes in the device input buffer} while ((dwNumBytesToRead == 0) && (ftStatus == FT_OK));//or Timeout
ftStatus = FT_Read(ftHandle, &byInputBuffer, dwNumBytesToRead, &dwNumBytesRead);//Read out the data from input buffer
printf("\n");printf("TI SN74BCT8244A IR default value is 0x81\n");printf("The value scanned by the FT2232H is 0x%x\n", byInputBuffer[dwNumBytesRead - 3]);printf("\n");printf("TI SN74BCT8244A DR bypass expected data is 00000010 = 0x2\n");printf("
The value scanned by the FT2232H = 0x%x\n", (byInputBuffer[dwNumBytesRead-1] >> 5));// Generate a clock while in Test-Logic-Reset// This will not do anything with the TAP in the Test-Logic-Reset state,//
but will demonstrate generation of clocks without any data transfer
byOutputBuffer[dwNumBytesToSend++] = 0x8F;// Generate clock pulses
byOutputBuffer[dwNumBytesToSend++] = 0x02;// (0x0002 + 1) * 8 = 24 clocks
byOutputBuffer[dwNumBytesToSend++] = 0x00;//
ftStatus = FT_Write(ftHandle, byOutputBuffer, dwNumBytesToSend, &dwNumBytesSent);// Send off the clock commands
dwNumBytesToSend = 0;// Reset output buffer pointerCopyright © 2009-2011 Future Technology Devices International Limited

9Document Reference No.: FT000183
Interfacing FTDI USB Hi-Speed Devices to a JTAG TAP Application Note AN_129
Version 1.1
Clearance No.: FTDI# 114/*// ----------------------------------------------------------// Start closing everything down// ----------------------------------------------------------*/
printf("\nJTAG program executed successfully.\n");printf("Press <Enter> to continue\n");getchar();// wait for a carriage return
FT_Close(ftHandle);// Close the port

return 0;// Exit with success}

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3.2 Program Output
The Texas Instruments example timing diagram is duplicated with an oscilloscope screen image:

Figure 3.1 – SN74BCT8244A timing example observation

Note that TDI/DO is always driven, and TDO/DI is pulled high by the SN74BCT8244A. The Texas
Instruments datasheet indicates several areas of “don’t care” which end up as logic “1” in this screen
shot.

TCK is generated without any activity on TDI, TDO or TMS.

Figure 3.2 – TCK generation

This is useful to run an internal test within a particular TAP. There are several options available which
include a specific number of pulses, or to pulse until a GPIO signal is set to a known value. In thisexample, 24 clocks are generated.

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4

Summary

The circuit and application program described in this application note demonstrate the basics ofestablishing communication with the MPSSE, configured for JTAG, on the FT2232H. In particular, thetiming diagram shown in the SN74BCT8244A datasheet is duplicated through an example program
utilizing the FTDI D2XX device driver to prove a known result.
As mentioned, the information in this application note also covers the FT232H and FT4232H withappropriate modifications to account for port selection and pin assignments.

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5

Acronyms and Abbreviations

Terms

Description
Multi-Protocol Synchronous Serial Engine – a state machine in certain FTDI USB

MPSSE

client devices that can be used to emulate serial protocols such as SPI, I2C and
JTAG
Joint Test Action Group – An industry organization responsible for generating a

JTAGstandard for in-circuit testing of complex circuits. JTAG is also commonly used inplace of the full specification name IEEE 1149.1

IEEE

IEEE 1149.1

Institute of Electrical and Electronics Engineers
Commonly referred to as “JTAG” – Industry standard describing building blocks
and software used to provide in-circuit test capabilities

Table 5.1 – Acronyms and Abbreviations

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6

Contact Information

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Vinculum is part of Future Technology Devices International Ltd. Neither the whole nor any part of the information contained in, or the
product described in this manual, may be adapted or reproduced in any material or electronic form without the prior written consent of
the copyright holder. This product and its documentation are supplied on an as-is basis and no warranty as to their suitability for any
particular purpose is either made or implied. Future Technology Devices International Ltd will not accept any claim for damages
howsoever arising as a result of use or failure of this product. Your statutory rights are not affected. This product or any variant of it is
not intended for use in any medical appliance, device or system in which the failure of the product might reasonably be expected toresult in personal injury. This document provides preliminary information that may be subject to change without notice. No freedom touse patents or other intellectual property rights is implied by the publication of this document. Future Technology Devices International
Ltd, Unit 1, 2 Seaward Place, Centurion Business Park, Glasgow G41 1HH United Kingdom. Scotland Registered Number: SC136640

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Appendix A - References
FT2232H Datasheet FTDI Ltd.
AN_108 Command Processor For MPSSE and MCU Host Bus Emulation Modes, Version 1.2 FTDI
Ltd.
AN_135 MPSSE Basics, FTDI Ltd.
AN_167 FT1248 Dynamic Parallel/Serial Interface Basics, FTDI Ltd.
Texas Instruments SN72BCT8244A Datasheet, © 1990, 1996
The Boundary-Scan Handbook, 3rd Ed., Kenneth P. Parker, © 2003, Kluwer Academic Publishers,
ISBN 1-4020-7496-4

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Version 1.1
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Appendix B - List of Figures and Tables
List of Figures
Figure 1.1 – IEEE 1149.1 (JTAG) state machine ......................................................... 3
Figure 1.2 – IEEE 1149.1 (JTAG) TAP chain ................................................................ 3
Figure 2.1 – Example circuit ....................................................................................... 5
Figure 3.1 – SN74BCT8244A timing example observation ........................................ 11
Figure 3.2 – TCK generation ..................................................................................... 11
List of Tables
Table 1.1 – SN74BCT8244 JTAG TAP registers ............................................................ 4
Table 2.1 – FT2232H JTAG pin assignments ............................................................... 5
Table 5.1 – Acronyms and Abbreviations .................................................................. 13

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Appendix C - Revision History
Revision History
Version 1.0 Initial Release

20th October, 2009

Version 1.1 Added references to FT232H

2nd September, 2011

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