Jljl_jljt_ri_rljl, Rn jttt, Mz 3500 – Sharp MZ-3500 User Manual

Page 85: D(k) st(k), Ack(c), D(c) st(c)

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MZ 3500

Command flag: "0" when succeedeing

8

bits are a key

data.

"V

when it is a command or a graphic control

data.

Data; Positive logic (negative logic on the cable)

Parity: Odd parity up to 27 bit from the correction flag.

2

)

Interfacing signals

CPU level

Positive logic

Active H

Active H

Positive logic

Active L

D(K): Output data from the keyboard.

ST{K): D(K) strobe signal. Also use for

interrupt to the CPU.

ACK(C): Acknowledge signal form the

CPU. Also use for the data

transfer

interrupt

disable

signal.

D(C); Output data from the CPU.

ST(C): D(C) strobe signal. Also use for

interrupt to the keyboard side.

3) Protocol

Key to sub CPU

Keyboard to the sub-CPU data transfer tapes place with

interrupt applied at every signal word (STK).

As the sub-CPU detects a next strobe (STK) after going

into the interrupt routine, it read data (K) as far as the

final parity bit, and the ACK (C) signal is sent back to

the keyboard side when the check-sum is correct.

If the ACK (C) signal returns with normal timing, the

keyboard controller accepts it. Unless the ACK signal

was detected, the same data is sent again assuming a

transmission error.

• Case when the error data link (sub-CPU not enable to

receive data properly) is established.

1) When parity error is found after the check-sum test.

2) When the sub-CPU is in execution of the NMI routine

or when NMI is applied during data tran..i.jj.

3) When an error is detected in the touting of strobe

(STK(K)) due to noise.

When one of above conditions is detected, data will be

sent again until received correctly. Key entries during

this periode are strobe in the key buffer. Should the key

buffer overflow, key entry will not be stored in the key

buffer.

• When a key buffer overflow is detected a KBOF error

code is inserted in the area vacant immediately after

transmission of one key-in data, without clear) ~ "

key buffer contents.

SUB CPU TO KEYBOARD

Basically the same as the above cases.

Data is 3 bits plus parity bit.

Return acknowledge pluse: Parity OK . .. STK

+

DK

Parity NO .. . STK only

KEY TO CPU (80C49, Z-80)

CPU level

D(K)

ST(K)

12.5

yiS

32.5*

AS

’ •

50

AS

.

*

50

AS

JLJl_JlJT_ri_rLJl

ACK(C)

SUB CPU T

'NT

17.5 Z's

22.5 AS

1

60~ 300 ns

1

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• CPU ^ KEY

D(C)

ST(C)

ST(K)

D ( K )

rn

JTTT

Cf\

7.5 AS (mm) /IS

(min)

50 — 90AS

17.5AS

(min)

17.5/IS

(min )

Jl

92

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