PAL20X10 PAL DESIGN SPECIFICATION PMSI408 JANE LEE(MMI)/KEN THOMAS(ZILOG) INTERFACE CONTROLLER FOR 68000 uP TO ZILOG 85XX PERIPHERALS MMI SUNNYVALE, CALIFORNIA
CLK /CS NC TEST /AS RW FC2 FCl FCO /RESET NC GND /OC /C3 /C2 /Cl /C0 /CYC NC /DTK /RD /WR /ACK VCC
C0 := /C0 * /TEST ; COUNT/HOLD (LSB)
Cl := /RESET * AS * Cl ;HOLD :+: /RESET * AS * C0 ;DECREMENT
C2 := /RESET * AS * C2 ;HOLD :+: /RESET * AS * C0 * Cl ;DECREMENT
C3 := /RESET * AS * C3 ;HOLD :+: /RESET * AS * C0 * Cl * C2 ; DECREMENT
DTK := /RESET * /ACK * CYC * C3 * /C2 * /Cl * C0 * CS ; DTACK FOR RD/WR CYCLE
+ /RESET * ACK * CYC * C3 * /C2 * Cl * /C0 ; DTACK FOR INTERRUPT CYCLE
CYC := /RESET* AS * /CYC * C0 ;START NEW CYCLE
+ /RESET* AS* CYC ;HOLD PROCESS OF CYCLE
:+: /RESET* CYC * DTK ;END OF CYCLE
RD := /RESET * CYC * /ACK * RW * C3 * /C2 * CS ; NORMAL READ OPERATION
+ /RESET * CYC * /ACK * RW * /C3 * C2 * Cl * C0 * CS ; NORMAL READ OPERATION
:+: /RESET * CYC * ACR * RW * C3 ; READ DURING INTERRUPT
+ RESET ; RESET
WR := /RESET * CYC * /ACK * /RW * C3 * /C2 * CS ; WRITE + /RESET * CYC * /ACK * /RW * /C3 * C2 * Cl * C0 * CS ; WRITE :+: RESET ; RESET
ACK := /RESET * FC0 * FC1 * FC2 * AS * CYC * /C0 ; START OF INTERRUPT ACKNOWLEDGE + /RESET * PC0 * FC1 * FC2 * CYC ; HOLDS INTERRUPT
FUNCTION TABLE
CLK /OC /RESET /C3 /C2 /Cl /CO TEST /CS FC2 FCl FC0 RW /AS /CYC /RD /WR /DTK /ACK
; / // ;C T/ FFF / C// DA ;L O/ CCCC SC CCC R A YRW TC ;E ER 3210 TS 210 W S CDR KK CYCLE COMMENTS C LL HHHH HH LLL H H HLL HH 1 INITIALIZATION C LH HHHL LH LLL H H HHH HH 2 C LH HHHH LH LLL H H HHH HH 3 C LH HHHL LL LLL H H HHH HH 4 C LH HHLH LL LLL H L LHH HH 5 BEGINNING OF WAIT FOR READ CYCLE C LH HHLL LL LLL H L LHH HH 6 C LH HLHH LL LLL H L LHH HH 7 C LH HLHL LL LLL H L LHH HH 8 C LH HLLH LL LLL H L LHH HH 9 C LH HLLL LL LLL H L LHH HH 10 C LH LHHH LL LLL H L LLH HH 11 /RD GOES ACTIVE C LH LHHL LL LLL H L LLH HH 12 C LH LHLH LL LLL H L LLH LH 13 ACKNOWLEDGE END OF DATA TRANSFER C LH LHLL LL LLL H L HLH HH 14 END OF READ CYCLE C LH HHHH LH LLL H H HHH HH 15 INITIALIZATION C LH HHHL LH LLL H H HHH HH 16 C LH HHLH LL LLL L L LHH HH 17 BEGINNING OF WAIT FOR WRITE CYCLE C LH HHLL LL LLL L L LHH HH 18 C LH HLHH LL LLL L L LHH HH 19 c LH HLHL LL LLL L L LHH HH 20 C LH HLLH LL LLL L L LHH HH 21 C LH HLLL LL LLL L L LHH HH 22 C LH LHHH LL LLL L L LHL HH 23 /WR GOES ACTIVE C LH LHHL LL LLL L L LHL HH 24 C LH LHLH LL LLL L L LHL LH 25 ACKNOWLEDGE END OF DATA TRANSFER C LH LHLL LL LLL L L HHL HH 26 END OF WRITE CYLE C LH HHHH LH LLL H H HHH HH 27 INITIALIZATION C LH HHHL LH LLL H H HHH HH 28 C LH HHLH LH HHH H L LHH HH 29 INTERRUPT CYCLE (WAITS RD SIGNAL) C LH HHLL LH HHH H L LHH HL 30 C LH HLHH LH HHH H L LHH HL 31 C LH HLHL LH HHH H L LHH HL 32 C LH HLLH LH HHH H I LHH HL 33 C LH HLLL LH HHH H L LHH HL 34 C LH LHHH LH HHH H L LHH HL 35 C LH LHHL LH HHH H L LLH HL 36 /RD GOES ACTIVE C LH LHLH LH HHH H L LLH HL 37 C LH LHLL LH HHH H L LLH LL 38 C LH LLHH LH HHH H L HLH HL 39 C LH HHHL LH LLL H H HHH HH 40 END OF CYCLE
The PAL provides a single chip interface controller for interfacing Motorola's 8 MHz 6800 microprocessor to Zilog's 4 MHz Z85XX peripheral. The interface controller generates all the required control signals, if which four /RD, /MR, PCLK (=/C0), and /ACK go to the Z85XX and /DTK goes to the 68000.
In addition to generating control signals, the interface controller has the capability of controlling three types of bus cycles; read, write, and interrupt acknowledge.
Timing for processing of data transfer is controlled with an internal down counter. A counter decoder controls timing of /DTK (data transfer acknowledge) to the 68000 to inform a complete data transfer cycle.
These operations are exercised in the function table and summarized in the operation table:
/C /// FFF //DCA OL/ ACR CCC WRTYC CKR SSW 210 RDKCK OPERATION Hxx XXX XXX ZZZZZ HI-Z LCL XXX XXX LLHHH INITIALIZATION LCH LLH LLL HLHLH READ LCH LLL LLL LHHLH WRITE LCH LHH HHH HLHLL READ DURING INTERRUPT
The PAL generates five control signals at which /RD, /MR, PCLK (=/C0), and /ACK to the Z85XX and /DTK goes to the 68000. /RD, /MR, and /ACK are three types of Z85XX cycles, which are controlled by the PAL:
/RD - read cycle /WR - write cycle /ACK - interrupt acknowledge cycle
/C0, /C1, /C2, and /C3 are part of a 4-bit synchronous down counter where /C3 is the MSB and /C0 is the LSB. /C0 is simply a divide by 2 of the 68000 clock used by the peripheral for PCLK. The other three signals, C1, C2, C3 with /CYC are used internal to the PAL for generating the above control signals.
The counter toggles between 14 and 15 until /CYC (=cycle) goes active low and then will begin counting down. The counter will continue counting down until /as goes inactive high, signalling the end of cycle. At this time the counter will go back to toggling between count 14 and 15. Refer to the function table.
The control signals, /RD, /WR, /ACK, and /DTK are generated through the pal and qualified with the counter to generate edges that meet time restraints.