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10.0 Local Processor Interface
10.2 Interface Pin Descriptions
RS8234
Datasheet for RS8234 xBR ServiceSAR
N8234DS1B
10.2 Interface Pin Descriptions
The local processor bus interface consists of the control, address, and status sig-
interface description, for further information on these interface pins.
Table 10-1. Processor Interface Pins
Signal
Dir(1)
Description
PROCMODE
I
Processor interface mode select input—A logic low on this input enables the local proces-
sor mode of operation.
PCS*
I
Processor interface chip select—A logic low on this signal in conjunction with a logic low
on PAS* at the rising edge of SYSCLK initiates a memory request to the memory controller.
PAS*
I
Processor address strobe— A logic low on this signal in conjunction with a logic low on
PCS* latches the value of PWNR, PBSEL[1,0], PADDR[1,0], and PBE[3:0]* at the rising
edge of SYSCLK.
PWNR
I
Processor write/read select—A logic one on this input indicates a write cycle, a logic zero
indicates a read cycle. Latched at rising edge of SYSCLK when PAS* and PCS* are active.
PADDR[1,0]
I
Word select address inputs—Indicates the word address for a single cycle access, or the
first word for a multi-cycle burst access. Latched at rising edge of SYSCLK when PAS* and
PCS* are active.
PBSEL[1,0]
I
Bank select inputs—Decode to select MCS[3:0]*. Latched at rising edge of SYSCLK when
PAS* and PCS* are active.
PBE[3:0]*
I
Byte select inputs—Active low. Allows individual bytes of selected word to be written. Not
active on reads. Latched at rising edge of SYSCLK when PAS* and PCS* active. PBE[3]*
controls writes to LDATA[31:24]; PBE[2]* controls LDATA[23:16]; etc.
PWAIT*
I
Processor wait input—Allows the processor to insert a variable number of wait states to
extend memory transaction. Must be active on rising edge of SYSCLK with PRDY* active to
insert wait cycle. May be used to interface to half speed or slow processor bus or to allow
the use of slow transceivers. If the insertion of wait states is not required, set this input to a
logic high. This signal may only be active, logic low, when PBLAST* is a logic high.
PBLAST*
I
Processor burst last input—Indicates the last word of a cycle. Must be active on rising
edge of SYSCLK with PRDY* active to indicate last cycle. If burst accesses and wait cycles
generated by PWAIT* are not required, this signal should be set to a logic low.
PRDY*
O
Processor interface ready signal—A logic low on this signal at rising edge of SYSCLK indi-
cates that the present cycle has been completed. If a read cycle, the data is valid to latch by
the processor; if a write cycle, the data has been written and may be removed from the bus.
When PRDY* is active, wait states may be inserted with PWAIT*, or a single or burst cycle
may be terminated by PBLAST*(2).
PFAIL*
I
The local processor can indicate a failure of its internal self-test or initialization processes
by asserting the PFAIL* input to the RS8234.
Notes: (1). Direction given with respect to the RS8234.
(2). This output corresponds to the READY* or RDYRCV* input in the i960 architecture.
(3). The processor system is responsible for controlling the direction of the bidirectional data bus transceiver. In the i960
architecture, this may be controlled by the DT/R* signal.