MITEL MT8920B Technical data

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ISO-CMOS ST-BUS FAMILY

MT8920B

ST-BUS Parallel Access Circuit

Features

• High speed parallel access to the serial ST-BUS

• Parallel bus optimized for 68000 µP (mode 1)

• Fast dual-port RAM access (mode 2) Access time: 120 nsec

• Parallel bus controller (mode 3) - no external

controller required

• Flexible interrupt capabilities - two

independent/programmable interrupt sources with auto-vectoring

• Selectable 24 and 32 channel operation

• Programmable loop-around modes

• Low power CMOS technology

Applications

• Parallel control/data access to T1/CEPT digital

trunk interfaces

• Digital signal processor interface to ST-BUS

• Computer to Digital PABX link

• Voice store and forward systems

• Interprocessor communications

ISSUE 7 March 1997

Ordering Information

MT8920BE 28 Pin Plastic DIP MT8920BP 28 Pin Plastic J-Lead MT8920BS 28 Pin SOIC

-40°C to 85°C

Description

The ST-BUS Parallel Access Circuit (STPA) provides a simple interface between Mitel’s ST-BUS and parallel system environments.

D7-D0

A4-A0

DS, OE

W, WE

DTACK,

BUSY, DCS

IRQ, 24/32

IACK, MS1

STCH

A5,

MMS

Parallel

Port

Interface

Interrupt

Registers

Control

Registers

Tx0

Dual Port Ram

32 X 8

Rx0

Dual Port Ram

32 X 8

Tx1

Dual Port Ram

32 X 8

Address

Generator

Figure 1 - Functional Block Diagram

Parallelto-serial

Converter

Serial-to-

Parallel

Converter

Parallelto-Serial

Converter

Comp/

MUX

STo0

STi0

STo1

F0i C4i

3-3

MT8920B CMOS

C4i

F0i

IACK, MS1

STi0

DS, OE

W, WE

A0 A1 A2 A3 A4

STCH

A5,

VSS

1 2

3 4

5 6

7 8

9 10 11 12 13 14

28 PIN PDIP/SOIC

VDD

MMS

DTACK, BUSY, DCS

IRQ, 24/32

STo1

STo0

DS, OE

W, WE

A0 A1 A2 A3

STi0 432

5 6 7 8 9 10 11

1213141516

28 PIN J-LEAD

F0i

IACK, MS1

C4i 1

•

D0D3D2

VSS

STCH A5,

VDD 28

MMS

DTACK,

BUSY, DCS

25 24 23 22 21 20 19

IRQ, 24/32 STo1 STo0 D7 D6 D5 D4

Figure 2 - Pin Connections

Pin Description

Pin # Name Description

1 C4i 4.096 MHz Clock. The ST-BUS timing clock used to establish bit cell boundaries f or the serial

bus.

2 F0i Framing Pulse. A low going pulse used to synchronize the STPA to the 2048 kbit/s ST-BUS

stream. The ﬁrst falling edge of C4i subsequent to the falling edge of F0i identiﬁes the start of a frame.

‡

3 IACK Interrupt Acknowledge (Mode 1). This active low input signals that the current b us cycle is

an interrupt vector fetch cycle. Upon receiving this acknowledgement, the STPA will output a user-programmed vector number on D0 - D7 indicating the source of the interrupt.

MS1 Mode Select 1 (Mode 2,3). This input is used to select the device operating modes. A low

applied to this pin will select mode 3 while a high will select mode 2. (Refer to Table 1.) 4 STi0 ST-BUS Input 0. This is the input for the 2048 kbit/s ST-BUS serial data stream. 5 CS Chip Select. This active low input is used to select the STPA for a parallel access . 6 DS Data Strobe (Mode 1). This active low input indicates to the STPA that v alid data is on the data

bus during a write operation or that the STPA must output valid data on the data bus during a

read operation.

OE Output Enable (Mode 2). This active low input enables the data bus driver outputs. OE Output Enable (Mode 3). This active low output indicates that the selected device is to be

read and that the data bus is available for data transfer. 7R/WRead/Write (Mode 1,2). This input deﬁnes the data bus transfer as a read (R/ W = 1) or a write

(R/W= 0) cycle.

WE Write Enable (Mode 3). This active low output indicates the data on the data bus is to be

written into the selected location of an external device.

8-12 A0-A4 Address Bus (Mode 1,2). These inputs are used to select the internal registers and two-port

memories of the STPA.

A0-A4 Address Bus (Mode 3). These address outputs are generated by the STPA and reﬂect the

position in internal RAM where the information will be fetched from or stored in. Addresses

generated in this mode are used to access external devices for direct memory transfer.

3-4

Pin Description (continued)

CMOS MT8920B

Pin # Name Description

‡

13 A5 Address Bit A5 (Mode 1). This input is used to extend the address range of the STPA. A5

selects internal registers when high and Tx/Rx RAM’s when low.

A5 Address Bit A5 (Mode 2). This input is used to extend the address range of the STPA. A5

selects Tx0/Rx0 RAM’s when low and Tx1/Rx0 RAM’s when high.

STCH Start of Channel (Mode 3). This signal is a low going pulse which indicates the start of an

ST-BUS channel. The pulse is four bits wide and begins at the start of each valid channel.

14 V

Ground.

15-22 D0-D7 Bidirectional Data Bus. This bus is used to transfer data to or from the STPA during a write

or read operation.

23 STo0 ST-B US Output 0. This output supplies the output ST-BUS 2048 kbit/s serial data stream from

Tx0 two-port RAM.

24 STo1 ST-BUS Output 1. In modes 1 and 2 this output supplies the output ST-BUS 2048 kbit/s serial

data stream from Tx1 two-port RAM. In mode 3, information arriving at STi0 is output here with one frame delay.

25 IRQ Interrupt Request (Mode 1). This open drain output, when low, indicates when an interrupt

condition has been raised within the STPA.

24/32 24 Channel/32 Channel Select (Mode 2,3). This input is used to select the channel

conﬁguration in modes 2 and 3. A low applied to this pin will select a 24 (T1) channel mode while a high will select a 32 (CEPT) channel mode.

26 DTACK Data Transfer Acknowledge (Mode 1). This open drain output is supplied by the STPA to

acknowledge the completion of data transfers back to the µP. On a read of the STPA, DTACK low indicates that the STPA has put valid data on the data bus. On a write, DTACK low indicates that the STPA has completed latching the µP’s data from the data bus.

BUSY BUSY (Mode 2). This open drain output signals that the controller and the ST-BUS are

accessing the same location in the dual-port RAM’s. It is intended to delay the controller access until after the ST-BUS completes its access.

DCS Delayed Chip Select (Mode 3). This low going pulse, which is four bit cells long, is active

during the last half of a valid channel. This signal is used to daisy-chain together two STPA’s in mode 3 that are accessing devices on the same parallel data bus.

27 MMS Master Mode Select (Reset). This Schmitt trigger input selects between either mode 1 (MMS

= 1), or modes 2and 3 (MMS = 0). If MMS is pulsed low in Mode 1 operation the control and interrupt registers will be reset. (Refer to Table 1.) During power-up, the time constant of the reset circuit (see Fig. 8) must be a minimum of ﬁve times the rise time of the power supply.

28 V

‡ Pin Descriptions pertain to all modes unless otherwise stated.

Mode MMS MS1

1 1 N/A µP

2 0 1 Fast RAM

300 Bus

Power Supply Input. (+5V).

Mode of

Operation

Peripheral

Mode

Controller

Mode

The STPA provides parallel-to-serial and serial-to-parallel conversions through a 68000-type interface. Two Tx RAMs and one Rx RAM are available along with full interrupt capability . 32 channel or 24 channel support is availab le . Control Register 1, bit D operation.

The STPA provides a fast access interface to Tx0, Tx1 and Rx0 RAMs. This mode is intended for full parallel support of 24 channel T1/ESF trunks and 32 channel CEPT trunks. Input channel operation.

The STPA will synchronously drive the parallel bus using the address generator and provide all data transfer signals. This mode is intended to support 24 or 32 channel devices in the absence of a parallel bus controller. Input operation, input

Function

(RAMCON) = 0 for 32 channel operation and D5 (RAMCON)= 1 for 24 channel

24/32 (pin 25) = 0 for 24 channel operation, input 24/32 (pin 25) = 1 for 32

24/32 (pin 25) = 0 for 24 channel

24/32 (pin 25) = 1 for 32 channel operation.

Table 1. STPA Modes of Operation

3-5

MT8920B CMOS

Functional Description

The STPA (ST-BUS Parallel Access) device provides a simple interface between Mitel’s ST-BUS and parallel system environments. The ST-BUS is a synchronous, time division, multiplexed serial bussing scheme with data streams operating at 2048 kbit/s. The ST-BUS is the primary means of access for voice, data and control information to Mitel’s family of digital telecommunications components, including North American and European digital tr unk interfaces, ISDN U and S digital line interfaces, ﬁlter codecs, rate adapters, etc. The STPA provides several modes of operation optimized according to the type of information being handled.

For interfacing parallel data and control information to the ST-BUS, such as signalling and link control for digital trunks, the STPA provides a µP access mode (Mode 1), and looks like a 68000 type peripheral. In this mode, the device provides powerful interrupt features, useful in monitoring digital trunk or line status (i.e., synchronization, alarms, etc.) or for setting up message communication links between microprocessors.

To interface high speed data or multi-channel voice/ data to the ST-BUS for switching or transmission, the STPA has a high speed synchronous access mode (Mode 2) and acts like a fast RAM. For voice storage and forward, bulk data transfer, data buffering and other similar applications, the STPA has a controllerless mode (Mode 3) in which it provides address and control signals to the parallel bus This is useful for performing direct transfers to the ST-BUS from external devices such as a RAM buffer.

The STPA is a two port device as shown in the functional block diagram in Figure 1. The parallel port provides direct access to three dual port RAM’s, two transmit and one receive. The address, data and

control busses are used to communicate between the RAM‘s and a parallel environment.

Two parallel-to-serial converters, and one serial-to-parallel converter interface the dual port RAM’s to the ST-BUS port of the STPA. This port consists of two serial output streams and one serial input stream operating at 2048 kbit/s. This conﬁguration of two outputs and one input was designed to allow a single STPA to form a complete control interface to Mitel’s digital trunk interfaces (MT8976, MT8978 and MT8979) which have two serial input and one serial output control streams.

ST-BUS clocking circuitry, address generator and various control and interrupt registers complete the STPA’s functionality.

Modes of Operation

The three basic modes of operation, µP Peripheral Mode (Mode 1), Fast RAM Mode (Mode 2) and Bus Controller Mode (Mode 3) are selected using two external input pins. These inputs are MMS and MS1 and are decoded as shown in Table 1. Whenever MMS=1 the device resides in Mode 1. In this mode, MS1 pin is unavailable and is used for a different function.

When MMS=0, Modes 2 or 3 are selected as determined by input MS1. If MS1=1, Mode 2 is selected and if MS1 =0, Mode 3 is selected.

Each of the modes of the STPA provides a different pinout to ease interfacing requirements of different parallel environments. These are shown in Figure 3 below. In µP Peripheral Mode the device uses interface signals consistent with a 68000-type µP bus. Mode 2, Fast RAM Mode, uses signals typical of standard RAM type interfaces. Mode 3 interface signals are very similiar to Mode 2 signals except that the address and control signals are supplied as outputs by the STPA.

3-6

µP Peripheral Mode #1

C4i

F0i

CS DS

W A0 A1 A2 A3

10 11 12 13 14

3 4 5

6 7 8 9

IACK

STi0

VSS

28 27 26 25 24 23 22 21 20 19 18 17 16 15

Mode #2 Bus Controller Mode #3

1 2

3 4 5

6 7 8 9

28 27 26 25 24 23 22 21 20 19 18 17 16 15

VDD MMS BUSY 24/32 STo1 STo0 D7 D6 D5 D4 D3 D2 D1 D0

VDD MMS DTACK IRQ STo1 STo0 D7 D6 D5 D4 D3 D2 D1 D0

C4i

F0i MS1 STi0

A0 A1 A2 A3 A4 A5

VSS

Fast RAM

10 11 12 13 14

Figure 3 - Modes 1, 2, 3 Pin Connections

C4i

F0i MS1 STi0

A0 A1 A2 A3 A4

STCH

VSS

10 11 12 13 14

1 2

3 4 5

6 7 8 9

28 27 26 25 24 23 22 21 20 19 18 17 16 15

VDD MMS DCS 24/32 STo1 STo0 D7 D6 D5 D4 D3 D2 D1 D0

CMOS MT8920B

24/32 Channel Operation

The STPA may be conﬁgured to operate as a 32 channel or 24 channel device. This feature, which is available in all three modes of operation, is particularly useful in applications involving data access to CEPT and T1 digital trunk interfaces.

When used as a data interface to Mitel‘s CEPT digital trunks, the STPA maps the 32 consecutive bytes of each dual port memory directly to ST-BUS channels 0-31. This is performed by the address generator shown in the functional block diagram (see Figure 1). Figures 4 c & d show the relationship between relative dual port RAM locations and corresponding ST-BUS channels, for both input and output serial streams, when the STPA is conﬁgured as a 32 channel device.

When used as a data interface to Mitel’s T1 trunk devices, however, only the ﬁrst 24 consecutive RAM locations are mapped to 24 of the 32 ST-BUS channels. This mapping follows a speciﬁc pattern which corresponds with the data streams used by Mitel‘s T1 products. Instead of a direct correlation (as in 32 channel operation), the 24 consecutive RAM locations are mapped to the ST-BUS with every fourth channel, beginning at channel 0, set to FF

(ie. channel 0, 4, 8, 12, 16, 20, 24 and 28). Figures 4 a & b show the relationship between RAM locations and ST-BUS channel conﬁguration. This feature allows the STPA to be interfaced directly to Mitel’s T1 trunk family.

When the STPA is operated in Mode 1, 24 and 32 channel conﬁgurations are selected using bit D (RAMCON) in Control Register 1. D5 = 0 selects 32 channel operation and D5 = 1 selects 24 channel operation. When the STPA is operated in Modes 2 or 3, however, the channel conﬁguration is done using input 24/32 (pin 25). When 24/32 = 1 the device uses all 32 channels and when 24/32 = 0 it uses 24.

lessened since ST-BUS accesses require only the last half cycle of C4i of every channel. When contention does occur, priority is always given to the ST-BUS access.

The STPA indicates this contention situation in a different manner for Modes 1 and 2. In Mode 1, the contention is masked by virtue of the "handshaking" method used to transfer data on this 68000-type interface. Data Strobe (DS) and Data Transfer Acknowledge (DTACK) control the exchange. If contention should occur the device will delay returning DTACK and thus stretch the bus cycle until the µP access can be completed.

In Mode 2, if access is attempted during a "contention window" the STPA will supply the BUSY signal to delay the start of the bus cycle. This “contention window” is deﬁned as shown in Figure

16. The window exists during the last cycle of C4i clock in each channel timeslot. Although ST-BUS access is only required during the last half of this clock period, the “contention window“ exists for the entire clock period since a parallel access occurring just prior to an ST-BUS access will not complete before the ST-BUS access begins. Figure 16 further shows four possible situations that may occur when parallel accesses are attempted in and around the “contention window”. Condition 1 indicates that an access occurring prior to the contention window but lasting into the ﬁrst half of it will complete normally with no contention arbitration. If the access should extend past the ﬁrst half of the contention window and into the ST-BUS access period, the BUSY signal will be generated. Conditions 3 and 4 show accesses occurring inside the contention window. These

accesses will result in BUSY becoming active immediately after the access is initiated and remaining active as shown in Figure 16.

Access contention is non-existent in Mode 3 since the parallel bus signals, driven by the STPA, are synchronized to the ST-BUS clocks.

Dual Port RAMS

Each of the three serial ST-BUS streams is interfaced to the parallel bus through a 32 byte dual port RAM. This allows parallel bus accesses to be performed asynchronously while accesses at the ST-BUS port are synchronous with ST-BUS clock. As with any dual port RAM interface between two asynchronous systems, the possibility of access contention exists. The STPA minimizes this occurrence by recognizing contention only when accesses are performed at the same time for the same 8-bit cell within the dual port RAM’s. Furthermore, the probability of contention is

Mode 1 - µP Peripheral Mode

In Mode 1, the STPA operates as an asynchronous 68000-type microprocessor peripheral. All three dual-port RAMS (Tx0, Tx1, Rx0) are made available and may be conﬁgured as 32 or 24 byte RAM’s. Also available are the full complement of control and interrupt registers. The address map for Mode 1 is shown in Table 2.

The STPA, in Mode 1, uses signals CS, R/W, DS (Data Strobe), DTACK (Data Acknowledge) IRQ, and IACK (Interrupt Acknowledge) at the parallel interface. The pinout of the device is shown in Figure 3.

3-7

MT8920B CMOS

29 30 31

25 26 27 28

21 22 23 24

17 18 19 20

29 30 31

25 26 27 28

21 22 23 24

17 18 19 20

13 14 15 16

9 101112

5678

1234 0

0 1 2 3 4 5 6 7 8 9 1011 121314 151617 181920 212223

13 14 15 16

9 101112

5678

Figure 4 a) RELATIVE Rx RAM ADDRESS vs. ST-BUS CHANNEL - 24 CHANNEL MODE

1234 0

Figure 4 b) RELATIVE Tx RAM ADDRESS vs. ST-BUS CHANNEL - 24 CHANNEL MODE

0 1 2 3 4 5 6 7 8 9 1011 121314 151617 181920 212223

012345678910111213141516171819202122232425262728293031

X- unused channels marked X transmit FF

Figure 4 c) RELATIVE Rx RAM ADDRESS vs. ST-BUS CHANNEL - 32 CHANNEL MODE

012345678910111213141516171819202122232425262728293031

Figure 4 d) RELATIVE Tx RAM ADDRESS vs. ST-BUS CHANNEL - 32 CHANNEL MODE

012345678910111213141516171819202122232425262728293031

3-8

STi0

RAM

RELATIVE

LOCATION

STo0

STo1

RAM

RELATIVE

LOCATION

STi0

RAM

RELATIVE

LOCATION

STo0

STo1

RAM

RELATIVE

LOCATION

CMOS MT8920B

ADDRESS BITS REGISTERS

•

1 X100000 Control Register 1 Control Register 1 X100001 Control Register 2 Control Register 2 X100010 Interrupt Vector Register Interrupt Vector Register X100100 Interrupt Flag Register 1 X100101 Interrupt Flag Register 2 X100110 Image Register 1 X100111 Image Register 2 X101000 Interrupt Mask Register 1 Interrupt Mask Register 1 X101001 Interrupt Mask Register 2 Interrupt Mask Register 2 X101010 Match Byte Register 1 Match Byte Register 1 X101011 Match Byte Register 2 Match Byte Register 2 X101100Interrupt Channel Address 1 Interrupt Channel Address 1 X101101Interrupt Channel Address 2 Interrupt Channel Address 2 1

•

Table 2. Mode 1 Address Map

NOTES:

X is don’t care A6 is bit D4 of Control Register 1

READ WRITE

Rx0 - Channel 0

•

Rx0 - Channel 31

Rx0 - Channel 0

•

Rx0 - Channel 31

Tx0 - Channel 0

Tx0 - Channel 31

Tx1 - Channel 0

Tx1 - Channel 31

•

Bit Name Description

7 (Unused) 6 IRQRST Interrupt Reset. This bit, when set high, automatically clears the Interrupt Flag Register

and the Interrupt Image Register without these registers being serviced. This bit automatically resets to zero after the register clear is completed.

5 RAMCON RAM Conﬁguration. This bit conﬁgures Tx0, Tx1 and Rx0 RAMS for 32 or 24 byte

operation. D5 = 0 for 32 channel; D5 = 1 for 24 channel.

Address Bit A6. This bit extends the addressing range for access to Tx1 memory.

3 IRQ2MODE Interrupt Source 2 Mode Select. This bit conﬁgures the source 2 interrupt generator.

D3 = 0 selects “static” interrupt mode; D3 = 1 selects “dynamic” interrupt mode.

2 IRQ1MODE Interrupt Source 1 Mode Select. This bit conﬁgures the source 1 interrupt generator.

D2 = 0 selects “static” interrupt mode; D2 = 1 selects “dynamic” interrupt mode. 1 IRQ2EN Interrupt Source 2 Enable. IRQ2EN = 1 enables interrupts to occur from source 2. 0 IRQ1EN Interrupt Source 1 Enable. IRQ1EN = 1 enables interrupts to occur from source 1.

Table 3. Control Register 1 Bit Deﬁnitions

3-9

MT8920B CMOS

Timing information for data transfers on this interface is shown in Figure 14. The Mode 1 interface is designed to operate directly with a 68000-type asynchronous bus but can easily accommodate most other popular microprocessors as well.

Control Registers

Two control registers allow control of Mode 1 features. Control Register 1 provides bits to select the type of interrupt, to enable interrupts from two different and independent sources and to reset the interrupt registers. Also contained in Control Register 1 are bits to conﬁgure the device for 24 or 32 channel operation and to expand the address range for convenient access to the second transmit RAM Tx1. A description of the bit functions in Control Register 1 is shown in Table 3.

Mode 1 provides various loopback paths and output conﬁguration options which are controlled by bits in Control Register 2. Bits D0, D1 of Control Register 2 conﬁgure loopbacks using input and output streams STi0, STo0 as described in Table 4. The input stream STi0 can be looped back to source the output stream STo0 as well as receive RAM Rx0. The transmit RAM Tx0 can be looped to source the receive RAM Rx0, as well as STo0 and, the transmit RAM Tx0 can be looped to the receive RAM Rx0 while STi0 sources STo0. The function of these loopback conﬁgurations is shown in Figure 5.

In a similar way, the output STo1 can be reconﬁgured for different functionality. Bits D2 and D3 of Control Register 2 allow STo1 to be sourced, with a one frame delay via Tx1 from receive stream STi0. STo1 can also output the result of a comparison of the contents of Tx1 ram with input stream STi0. These output conﬁgurations of STo1 are shown in Figure 6

a and b. Figure 6 c shows the effect of combining these two features.

Interrupt Registers

Interrupts can be generated in Mode 1 only. Two channels of the ST-BUS input stream, STi0, can be selected to provide an interrupt to the system. Interrupts can be of two types: Static or Dynamic. Static interrupts are caused when data within a selected channel matches a given pattern. Dynamic interrupts occur when bits in a selected channel change state (1 to 0, 0 to 1 or toggle). Interrupts are controlled through two identical paths (1 and 2) consisting of the following registers:

Interrupt Channel Address (1/2): The address (0-31) of the channel which will generate the interrupt is stored in this register.

Image Register (1/2): The contents of the channel causing the interrupt is stored in this register. Reading this register will clear its contents.

Match Byte Register (1/2): In static mode this register is used to store the byte which will be compared with the contents of the selected channel causing the interrupt.

In dynamic mode, the bits in this register and the corresponding bit in the Interrupt Mask Register deﬁne the type of dynamic interrupt (i.e., 0 to 1, 1 to 0, toggle). (Refer to Table 5.)

Bit Name Description

7-4 (Unused) 3-2 CONFIG STo1 Output Conﬁguration Bits:

D3D2 = 00- Normal operation. ST-BUS stream from Tx1 is output on STo1 pin.

01- STi0 stream is output on STo1 pin delayed one frame (Figure 6 a). 10- STi0 is compared through XOR (exclusive OR) with ST-BUS stream

from Tx1 and output at STo1 (Figure 6 b).

11- STi0 stream, delayed one frame (via Tx1), is compared (XOR) with the

next frame arriving at STi0 and the result output at STo1 (Figure 6 c).

1-0 LOOPBACK Internal Loopback Conﬁguration Bits:

D1D0 = 00- Normal operation. No internal loops.

01- Loop STi0 to STo0 while still receiving STi0 in Rx0 (Figure 5 a). 10- Loop Tx0 output ST-BUS stream to Rx0 input ST-BUS stream while

outputting Tx0 output to STo0. STi0 is not received (Figure 5 b).

11- Loop Tx0 output ST-BUS stream to Rx0 input ST-BUS stream. Loop

STi0 to STo0 (Figure 5 c).

Table 4. Control Register 2 Bit Deﬁnitions

3-10

Control Register 2 Bits D1 = 0, D0 = 1

Control Register 2

= 0, D2 = 1

Bits D

CMOS MT8920B

µP

Control Register 2

= 1, D0 = 0

Bits D

µP

Control Register 2 Bits D

= 1, D0 = 1

µP

Tx0

Rx0

Tx0

Rx0

µP

STo0

STi0Rx0

Control Register 2

= 1, D2 = 0

Bits D

STo0

STi0

STo0

STi0

µP

Control Register 2 Bits D3 = 1, D2 = 1

µP

Tx0

Rx0

Tx1

Tx0

Rx0

Tx1

Tx0

Rx0

Tx1

1 Frame Delay

STo0

STi0

STo1

STo0

STi0

STo1

STo0

STi0

STo1

Figure 5 - Loopback Conﬁgurations

Interrupt Mask Register (1/2): In static mode the

contents of this register masks bits in the Match Byte Register that are ’don’t care’ bits

1 - bit masked 0 - bit not masked

In dynamic mode, each bit in this register and the corresponding bit in the Match Byte Register deﬁne what type of dynamic interrupt is selected. (Refer to Table 5.)

Interrupt Flag Register (1/2): In static mode the least signiﬁcant bit in this register is set to 1 to ﬂag the corresponding path in which the interrupt occurs.

In dynamic mode this register sets the bits which reﬂect the position of the bits in the corresponding Interrupt Register which caused the interrupt.

Figure 6 - STo1 Conﬁgurations

Interrupt Vector Register

This register shown in Figure 7 is common to both interrupt paths and stores an 8 bit vector number which will be output on the data bus when Interrupt Acknowledge (IACK) is asserted. Bits labelled V2- V7 are stored by the controlling µP. Bits IRQ1 and IRQ2 are set by the STPA to indicate which path caused the interrupt. This creates unique vectors which are used by the µP to vector to interrupt service routines. This feature may be bypassed by simply not asserting IACK during interrupt acknowledged.

D7 D6 D5 D4 D3 D2 D1 D0

V2IRQ2 IRQ1

Figure 7 - Interrupt Vector Registers

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