Abstract:
A repeater circuit configured to duplicate or otherwise coordinate signal transitions between state conductors, such as for use in asynchronous communication systems. The repeater circuit may include a state node or other feature to facilitate enforcing or otherwise ordering transitioning of the state conductors.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to repeater circuits, such as but not limited to those suitable for use with single track handshaking wires. 
         [0003]    2. Background Art 
         [0004]    A repeater circuit can be used with single track handshaking wires and other transmission mediums to facilitate transmitting signals from one location on a “left” side of the repeater to another location on a “right” side of the repeater. One optional and commonly used configuration may include the repeater pulling up/down the right side if an external circuit pulls up/down the left side and/or pulling down/up the left side if an external circuit pulls down/up the right side. This type of an arrangement may be suitable for use with GasP, other single wire handshake communication protocols, and other circuits where a request signal is used to pull up the left side of the repeater and a subsequent acknowledge signal is used to pull down the right side after the repeater relays the request signal to the right side, i.e., after the right side is pulled up. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIGS. 1-6  illustrate a number of repeater circuits. 
       
    
    
     DETAILED DESCRIPTION 
       [0006]      FIG. 1  illustrates a repeater circuit  10  configured to duplicate signal transitions on either a left side state conductor L or a right side state conductor R to the other. The repeater circuits  10  is predominately described with respect to duplicating a request transition on the left side L to the right side R and duplicating or simulating an acknowledge request from the right side R to the left side L. This methodology may be employed in systems having asynchronous hand-shaking protocols, such as but not limited to GasP systems, and other systems where receipt of a request signals is typically replied to with an acknowledge signal. Of course, the repeater circuit  10  is not intended to be so limited and fully contemplates its use and application to any type of circuit arrangement. 
         [0007]    The state conductors L, R may be connected to any type of external elements suitable for use with the repeater  10 . The external circuits may be configured to indicate the request signals with a falling transition, or low, and the acknowledge signal with a rising transition, or high. The transitions may be generally described as changing the state of the conductors, i.e., from a high to low or from a low to high. Upon the left side L receiving the falling transition, a NOR gate Nr 1  receives a low input from the left state conductor L and another low input from a state node S, which in turn causes the NOR gate Nr 1  to activate n-type transistor Nr to pull the right state conductor R low, thereby duplicating the falling transition on the left state conductor L to the right state conductor R. 
         [0008]    A master clear or other feature (not shown) may be included to initially set the state node S to a desired high or low value depending on the transitioning state of the left and right state conductors. If the left and right terminals are high at start-up, then the state node S should be cleared to low. The terminal, in this case the left terminal L that connects to the input of the NOR gate Nr 1 , must receive the first transition and it must be a rising transition. Once the request signal is duplicated to the right state conductor R, the P-type transistor Ps is activated to pull the state node S from its previous low state to a high state. A keeper circuit may be include to maintain this state until the repeater  10  receives the next transition signal. After each transition occurs, the state of node S changes. The purpose of this state node S is to remember the last transition that is repeated and to enforce what the next transition must be, i.e. after a rising transition on the left terminal L is repeated to the right terminal R, the next transition to be repeated must originate on the right terminal R, be repeated to the left terminal L, and be a falling transition. The transition of the state node after duplicating the rising transition to the right state conductor and maintaining the transition state of the state node allows for maintaining state. 
         [0009]    The external circuit associated with the right state conductor R may instigate a transition on the right state conductor R in order to acknowledge receipt of the request signal, which in this case requires transitioning the right state conductor from a low to a high. The high transition of the right side state conductor R and the high value at the state node S activates a NAND gate Nd 1  to activate a P-type transistor P 1 , which in turns pulls the left side state conductor L high, thereby duplicating the rising transition on the right state conductor R to the left side state conductor L. The high transition on the left side state conductor L then activates an n-type transistor Ns to pull the state node S back low, thereby setting the repeater  10  to subsequently duplicate another falling transition from the left side state conductor L to the right side state conductor R. 
         [0010]      FIG. 2  illustrates a repeater circuit  20  configured to copy a request transition on a left state conductor L to right state conductors R 1  and R 2 . The repeater  20  may be further configured to wait for acknowledge transitions on both of the first and second right state conductors R 1  and R 2  before instigating the acknowledge transition on the left state conductor L. 
         [0011]    A transistor n 1  may be included for transitioning the left conductor L from a high state to a low state in order to communicate an acknowledge signal from the right side. The pull of the transistor n 1  is opposite to the pull of the associated external element that pulls the left conductor L from low to high when sending the request signal. Transistors p 1 , p 2  may be included for respectively transitioning the right state conductors R 1 , R 2  from a low to high when communicating the request signal from the left side. The pull of the transistors p 1 , p 2  is opposite to the pull of the associated external element that pulls the conductors R 1 , R 2  from high to low when sending the acknowledge signal. 
         [0012]    A state node S and keeper circuit k may be included to add state to the repeater  20 . The state of the state node may be used to selectively enable the transistors n 1 , p 1 , and p 2 . The transistor n 1  may be used to transition the first state conductor to indicate an acknowledge signal from either one of the right side state conductors R 1 , R 2  if the state node is low and the external elements transition both the state conductors R 1 , R 2  to send the acknowledge signal. The transistors p 1 , p 2  may be used in a similar manner to transition the right state conductors R 1 , R 2  to indicate the request signal from the left side if the state node S is high and the external element transitions the left state conductor L to communicate the request signal. 
         [0013]    State transistors Ns, Ps may be included to manage the state of the state node s. The transistors Ns, Ps may be configured to pull the state node S between its high and low states. The state transistor Ps may be used to pull the state node to the high state if the transistor n 1  transitions the left state conductor. The state transistor Ns may pull the state node S low if the transistors p 1 , p 2  transition the right state conductors R 1 , R 2 . 
         [0014]      FIG. 3  illustrates a repeater circuit  30  configured such that transitions caused by one of the external elements on the left state conductor are alternately toggled to the two right state conductors R 1 , R 2 , such as to communicate the request signal from the left to the right side of the repeater  30 . This may, for example, include communicating the request signal to state conductor R 1  and then alternately communicating the next request signal to the state conductor R 2 . The acknowledge signals associated with each request signal may be communicated to the left state conductor L from the toggled to conductor R 1 , R 2  such that only the conductor R 1 , R 2  receiving the request signal is used to communicate the acknowledge signal. 
         [0015]    Transistors n 1 , n 2 , p 1 , and p 2  may be included for transitioning the conductors L, R 1 , and R 2 . The transistor n 1  may be used to pull the left conductor L from high to low in order to communicate the acknowledge signal from one of the right conductors R 1 , R 2 . The pull of the transistor n 1  is opposite to the pull of the associated external element that pulls the left conductor L from low to high when sending the request signal. Transistor p 1 , p 2  may be included for respectively transitioning the right state conductors R 1 , R 2  from a low to a high in order to communicate the request signal. The pull of the transistors p 1 , p 2  is opposite to the pull of the associated external element that pulls the conductors R 1 , R 2  from high to low when sending the acknowledge signal. 
         [0016]    State nodes S 1 , S 2  and keeper circuits k 1 , k 2  may be included to add state to the repeater  30 . The state of the state nodes S 1 , S 2  may be used to selectively enable the transistors n 1 , p 1 , p 2 . The transistors and state nodes may be configured such that the transistors n 1 , n 2  only transition the left state conductor to communicate the acknowledge signal if the state node S 1  is low and the toggled to state conductor R 1 , R 2 , i.e., the conductor receiving the request signals, is transitioned by the external element used to the send the acknowledge signal. This allows the repeater  30  to require the acknowledge signal from the toggled to conductor R 1 , R 2  receiving the request signal and not the other conductor R 1 , R 2  that does not receive the request signal. 
         [0017]    The transistor n 1  may be used to pull the left conductor L low if the state node s 1  is low and the external element transitions the conductor R 1 . The transistor n 2  may be used to pull the left conductor L low if the state node S 1  is low and the external element transition the conductor R 2 . The transistor p 1  may be used to transition the conductor R 1  if the state nodes S 1 , S 2  are high and the external element transitions the conductor L high. The transistor p 2  may be used to transition the conductor R 2  if the state node S 1  is high, the state node S 2  is low, and the external element transitions the conductor L high. 
         [0018]    Transistors n 3   a , n 3   b , p 3 , p 4 , and n 4  may be included to manage the state of the state nodes S 1 , S 2 . The transistors may be configured to pull the state nodes S 1 , S 2  between high and low states. The transistor p 3  may be used to pull the state node S 1  high if either of the transistors n 1 , n 2  transitions the left conductor L. The transistor n 3   a , n 3   b  may be used to pull the state node S 1  low if with of the conductors R 1 , R 2  are pulled high. The transistor p 4  may be used to pull the state node S 2  high if the transistor p 2  transitions the conductor R 2 . The transistor n 4  may be used to pull the state node S 2  low if the transistor p 1  transitions the conductor R 1 . This repeater  30  may provided the following order of events: L high, R 1  high, R 1  low, L low, L high, R 2  high, R 2  low, L low. 
         [0019]      FIG. 4  illustrates a repeater circuit  40  configured such that a transition caused by the external element on the conductor L is duplicated to the conductor R and a second subsequent transition caused by the external element on the conductor L results in immediately transitioning of the conductor L without transitioning the conductor R. This arrangement may be used to communicate a request from the left to the right, receive a corresponding acknowledge from the right and communicate it to the left, then receive a second request on the left and immediately communicate an acknowledge to the left without ever communicating the request to the right upon receipt of the next request. 
         [0020]    Transistors n 1 , n 2 , and p 3  may be included for transitioning the conductors L, R. The transistors n 1 , n 2  may be used to pull the left conductor L low when communicating the acknowledge signal. The pull of the transistor n 1  is opposite to the pull of the associated external element that pulls the left conductor L high when sending the request signal. Transistor p 3  may be included for transitioning the conductors R from a low to a high when communicating the request signal. The pull of the transistor p 3  is opposite to the pull of the associated external element that pulls the conductors R 1 , R 2  low when sending the acknowledge signal. 
         [0021]    State nodes S 1 , S 2 , optionally with the assistance of keeper circuits k 1 , k 2 , may be included to hold state of the repeater  40 . The state of the state nodes S 1 , S 2  may be used to selectively enable the transistors n 1 , n 2 , p 3 . The transistor n 2  may be used to pull the conductor L low if the state node S 1  is low and external element pulls the conductor R low. The transistor n 1  may be used to pull the conductor L low if the state nodes S 1  and S 2  are high and conductor L is high, which pulls the conductor L low without requiring the conductor R to communicate the acknowledge signal. The transistor p 3  may be used to pull the conductor R high if the conductor L and state node S 1  are high and the state node S 2  is low. The state of the state nodes S 1 , S 2 , and in particular, S 2 , controls whether the conductor R receives the request signal and whether the acknowledge signal is received without transitioning the conductor r. 
         [0022]    Transistors p 2 , n 3 , n 6 , and n 7  may be included to manage the state of the state nodes S 1 , S 2 . The transistors may be configured to pull the state nodes S 1 , S 2  between high and low states. The transistor p 3  may be used to pull the state node S 1  high if either one of the transistors nil, n 2  pulls the conductor L low. The transistor n 3  may be used to pull the state node S 1  low if the conductor R is transitioned with an acknowledge signal. The transistor n 6  may be used to pull the state node S 2  low if the transistor n 1  is used to transition the conductor L. The transistor p 7  may be used to pull the state node S 2  low if the transistor p 3  is used to transition the conductor R. 
         [0023]    The use of the state nodes S 1 , S 2  and the configuration of the various transistors allows the repeater  40  to operate in a system when each request must be answered with an acknowledgment. The repeater  40  is helpful in that each request is answered but only every other request is actually communicated to the right side.  FIG. 5  illustrates a repeater circuit  50  having two the repeater  50  describer above with respect to  FIG. 4 . The additional repeater  50  adds an additional cycle to the cycle described above such that only every fourth request is communicated from the additional repeater circuit  50 . 
         [0024]      FIG. 6  illustrates another repeater circuit  60  configured to include a condition bit. The state of the condition bit can be used to allow or prohibit transitions caused by one of the external elements on one of the state conductors to be duplicated to the other state conductor. 
         [0025]    As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary and they may be embodied in various and alternative forms. The figures are not necessarily to scale, some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for the claims and/or as a representative basis for teaching one skilled in the art. 
         [0026]    While embodiments have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the embodiments. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the embodiments.